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 are                  100 m^2
 liter                 1000 cc      The liter was defined in 1901 as the
 oldliter[?]              1.000028 dm^3  space occupied by 1 kg of pure water at
 l                     liter        the temperature of its maximum density
under a pressure of 1 atm. This was supposed to be 1000 cubic cm, but it was discovered that the original measurement was off. In 1964, the liter was redefined to be exactly 1000 cubic centimeters.
 mho                   siemens   Inverse of ohm, hence ohm spelled backward
 galvat[?]                ampere    Named after Luigi Galvani
 angstrom              1e-10 m   Convenient for describing molecular sizes
 xunit[?]                 1.00202e-13 meter  Used for measuring wavelengths
 siegbahn[?]              xunit            of X-rays.  It is defined to be
1|3029.45 of the spacing of calcite planes at 18 degC. It was intended to be exactly 1e-13 m, but was later found to be off slightly.
 fermi                 1e-15 m   Convenient for describing nuclear sizes
Nuclear radius is from 1 to 10 fermis
 barn                  1e-28 m^2  Used to measure cross section for
particle physics collision, said to have originated in the phrase "big as a barn".
 shed[?]                  1e-24 barn  Defined to be a smaller companion to the
barn, but it's too small to be of much use.
 brewster              micron^2/N  measures stress-optical coef
 diopter               /m        measures reciprocal of lens focal length
 fresnel[?]               1e12 Hz   occasionally used in spectroscopy
 shake[?]                 1e-8 sec
 svedberg              1e-13 s   Used for measuring the sedimentation
coefficient for centrifuging.
 gamma                 microgram
 lambda                microliter
 spat[?]                  1e12 m    Rarely used for astronomical measurements
 preece[?]                1e13 ohm m  resistivity
 planck[?]                J s       action of one joule over one second
 sturgeon              /henry    magnetic reluctance
 daraf[?]                 1/farad   elastance (farad spelled backwards)
 leo                   10 m/s^2
 poiseuille[?]            N s / m^2  viscosity
 mayer[?]                 J/g K     specific heat
 mired[?]                 / microK  reciprocal color temperature.  The name
abbreviates micro reciprocal degree.
 metricounce[?]           25 g
 mounce[?]                metricounce
 finsenunit[?]            1e5 W/m^2  Measures intensity of ultraviolet light
with wavelength 296.7 nm.
 fluxunit[?]              1e-26 W/m^2 Hz  Used in radio astronomy to measure
the energy incident on the receiving body across a specified frequency bandwidth. [12]
 jansky                fluxunit  K. G. Jansky identified radio waves coming
 Jy[?]                    jansky    from outer space in 1931.
 pfu[?]                  / cm^2 sr s  particle flux unit -- Used to measure
rate at which particles are received by a spacecraft as particles per solid angle per detector area per second. [18]
 katal                 mol/sec   Measure of the amount of a catalyst.  One
 kat[?]                   katal       katal of catalyst enables the reaction
to consume or produce on mol/sec.

 minute                60 s
 min                   minute
 hour                  60 min
 hr                    hour
 day                   24 hr
 d                     day
 da                    day
 week                  7 day
 wk[?]                    week
 sennight[?]              7 day
 fortnight             14 day
 blink[?]                 1e-5 day  Actual human blink takes 1|3 second
 ce[?]                    1e-2 day
 cron[?]                  1e6 years
 watch                 4 hours   time a sentry stands watch or a ship's
crew is on duty.
 bell                  1|8 watch  Bell would be sounded every 30 minutes.

 circle                2 pi radian
 degree                1|360 circle
 arcdeg[?]                degree
 arcmin[?]                1|60 degree
 arcminute             arcmin
 arcsec                1|60 arcmin
 arcsecond             arcsec
 quadrant[?]              1|4 circle
 quintant[?]              1|5 circle
 sextant               1|6 circle

 pulsatance[?]            radian / sec
 gon                   1|100 rightangle  measure of grade
 grade                 gon
 centesimalminute[?]      1|100 grade
 centesimalsecond[?]      1|100 centesimalminute
 milangle[?]              1|6400 circle    Official NIST definition.
Another choice is 1e-3 radian.
 pointangle[?]            1|32 circle  Used for reporting compass readings
 centrad[?]               0.01 radian  Used for angular deviation of light
through a prism.
 mas[?]                   milli-arcsec  Used by astronomers
 seclongitude[?]          circle (seconds/day)  Astronomers measure longitude
(which they call right ascension) in time units by dividing the equator into 24 hours instead of 360 degrees.

 Solid angle measure

 sphere                4 pi sr
 squaredegree[?]          1|180^2 pi^2 sr
 squareminute[?]          1|60^2 squaredegree
 squaresecond[?]          1|60^2 squareminute
 squarearcmin[?]          squareminute
 squarearcsec[?]          squaresecond
 sphericalrightangle[?]   0.5 pi sr
 octant[?]                0.5 pi sr 

 Concentration measures

 percent               0.01
 mill                  0.001    Originally established by Congress in 1791
as a unit of money equal to 0.001 dollars, it has come to refer to 0.001 in general. Used by some towns to set their property tax rate, and written with a symbol similar to the % symbol but with two 0's in the denominator. [18]
 proof                 1|200    Alcohol content measured by volume at
60 degrees Fahrenheit. This is a USA measure. In Europe proof=percent.
 ppm                   1e-6
 partspermillion[?]       ppm
 ppb[?]                   1e-9
 partsperbillion[?]       ppb      USA billion
 ppt[?]                   1e-12
 partspertrillion[?]      ppt      USA trillion
 karat                 1|24     measure of gold purity
 caratgold[?]             karat
 gammil[?]                mg/l
 basispoint[?]            0.01 %   Used in finance
 fine                  1|1000   Measure of gold purity 

 The pH scale is used to measure the concentration of hydronium (H3O+) ions in
 a solution.  A neutral solution has a pH of 7 as a result of dissociated
 water molecules.

 pH     pH(x) [;mol/liter] 10^(-x) mol/liter ; (-log(pH liters/mol))


 Two types of units are defined: units for computing temperature differences
 and functions for converting absolute temperatures.  Conversions for
 differences start with "deg" and conversions for absolute temperature start
 with "temp".

 °F          tempF(x) [;K] (x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32

 °K[?]           tempC(x) [;K] x K + stdtemp ; (tempC +(-stdtemp))/K  In 1741 Anders Celsius
 °C            tempcelsius(x) [;K] tempC(x); ~tempC(tempcelsius)  introduced a temperature
 degcelsius[?]            K        scale with water boiling at 0 degrees and
                           K        freezing at 100 degrees at standard
pressure. After his death the fixed points were reversed and the scale was called the centigrade scale. Due to the difficulty of accurately measuring the temperature of melting ice at standard pressure, the centigrade scale was replaced in 1954 by the Celsius scale which is defined by subtracting 273.15 from the temperature in Kelvins. This definition differed slightly from the old centigrade definition, but the Kelvin scale depends on the triple point of water rather than a melting point, so it can be measured accurately.

 fahrenheit         5|9 degC  Fahrenheit defined his temperature scale
                        5|9 degC  by setting 0 to the coldest temperature
he could produce in his lab with a salt water solution and by setting 96 degrees to body heat. In Fahrenheit's words:

Placing the thermometer in a mixture of sal ammoniac or sea salt, ice, and water a point on the scale will be found which is denoted as zero. A second point is obtained if the same mixture is used without salt. Denote this position as 30. A third point, designated as 96, is obtained if the thermometer is placed in the mouth so as to acquire the heat of a healthy man." (D. G. Fahrenheit, Phil. Trans. (London) 33, 78, 1724)

 rankine        degF             The Rankine scale has the
            degreesrankine   Fahrenheit degree, but it's zero
            degF             is at absolute zero.

 reaumur            10|8 degC  The Reaumur scale was used in Europe and
particularly in France. It is defined to be 0 at the freezing point of water and 80 at the boiling point. Reaumur apparently selected 80 because it is divisible by many numbers.

 Units cannot handle wind chill or heat index because they are two variable
 functions, but they are included here for your edification.  Clearly these
 equations are the result of a model fitting operation.

 wind chill index (WCI) a measurement of the combined cooling effect of low
      air temperature and wind on the human body. The index was first defined
      by the American Antarctic explorer Paul Siple in 1939. As currently used
      by U.S. meteorologists, the wind chill index is computed from the
      temperature T (in °F) and wind speed V (in mi/hr) using the formula:
WCI = 0.0817(3.71 sqrt(V) + 5.81 - 0.25V)(T - 91.4) + 91.4.
      For very low wind speeds, below 4 mi/hr, the WCI is actually higher than
      the air temperature, but for higher wind speeds it is lower than the air

 heat index (HI or HX) a measure of the combined effect of heat and
      humidity on the human body. U.S. meteorologists compute the index
      from the temperature T (in °F) and the relative humidity H (as a
      value from 0 to 1).
HI = -42.379 + 2.04901523 T + 1014.333127 H - 22.475541 TH - .00683783 T^2 - 548.1717 H^2 + 0.122874 T^2 H + 8.5282 T H^2 - 0.0199 T^2 H^2.

 Physical constants

 Basic constants

 pi                    3.14159265358979323846
 c                     2.99792458e8 m/s  speed of light in vacuum (exact)
 light                 c
 mu0[?]                   4 pi 1e-7 H/m   permeability of vacuum (exact)
 epsilon0[?]              1/mu0 c^2       permittivity of vacuum (exact)
 energy                c^2             convert mass to energy
 e                    1.602176462e-19 C  electron charge
 h                   6.62606876e-34 J s  Planck constant
 hbar[?]                  h / 2 pi
 spin                  hbar
 coulombconst[?]          1/4 pi epsilon0  listed as "k" sometimes
 Physico-chemical constants

 atomicmassunit[?]        1.66053873e-27 kg atomic mass unit (defined to be
 u                     atomicmassunit    1|12 of the mass of carbon 12)
 amu                   atomicmassunit
 amu_chem[?]              1.66026e-27 kg  1|16 of the weighted average mass of
the 3 naturally occuring neutral

isotopes of oxygen

 amu_phys[?]              1.65981e-27 kg  1|16 of the mass of a neutral
oxygen 16 atom
 dalton                u               Maybe this should be amu_chem?
 avogadro              grams/amu mol   size of a mole
 N_A[?]                   avogadro
 gasconstant[?]         8.314472 J / mol K  molar gas constant
 R                     gasconstant
 boltzmann             R / N_A         Boltzmann constant
 k                     boltzmann
 molarvolume[?]       mol R stdtemp / atm  Volume occupied by one mole of an
ideal gas at STP.
 loschmidt[?]   avogadro mol / molarvolume  Molecules per cubic meter of an
ideal gas at STP. Loschmidt did work similar to Avogadro.
 stefanboltzmann[?] pi^2 k^4 / 60 hbar^3 c^2  The power per area radiated by a
 sigma                 stefanboltzmann   blackbody at temperature T is
given by sigma T^4.
 wiendisplacement[?]      2.8977686e-3 m K  Wien's Displacement Law gives the
frequency at which the the Planck spectrum has maximum intensity. The relation is lambda T = b where lambda is wavelength, T is temperature and b is the Wien displacement. This relation is used to determine the temperature of stars.
 K_J[?]  483597.9 GHz/V  Direct measurement of the volt is difficult.  Until
recently, laboratories kept Weston cadmium cells as a reference, but they could drift. In 1987 the CGPM officially recommended the use of the Josephson effect as a laboratory representation of the volt. The Josephson effect occurs when two superconductors are separated by a thin insulating layer. A "supercurrent" flows across the insulator with a frequency that depends on the potential applied across the superconductors. This frequency can be very accurately measured. The Josephson constant K_J, which is equal to 2e/h, relates the measured frequency to the potential. The value given here is the officially specified value for use beginning in 1990. The 1998 recommended value of the constant is 483597.898 GHz/V.
 R_K[?]  25812.807 ohm   Measurement of the ohm also presents difficulties.
The old approach involved maintaining resistances that were subject to drift. The new standard is based on the Hall effect. When a current carrying ribbon is placed in a magnetic field, a potential difference develops across the ribbon. The ratio of the potential difference to the current is called the Hall resistance. Klaus von Klitzing discovered in 1980 that the Hall resistance varies in discrete jumps when the magnetic field is very large and the temperature very low. This enables accurate realization of the resistance h/e^2 in the lab. The value given here is the officially specified value for use beginning in 1990.

 Various conventional values

 Hg           13.5951 gram force / cm^3  Standard weight of mercury (exact)
 water                 gram force/cm^3  Standard weight of water (exact)
 waterdensity[?]          gram / cm^3     Density of water

 mach                  331.46 m/s      speed of sound in dry air at STP

 Atomic constants

 Rinfinity[?]             10973731.568 /m  The wavelengths of a spectral series
 R_H[?]                   10967760 /m       can be expressed as
1/lambda = R (1/m^2 - 1/n^2). where R is a number that various slightly from element to element. For hydrogen, R_H is the value, and for heavy elements, the value approaches Rinfinity, which can be computed from m_e c alpha^2 / 2 h with a loss of 5 digits of precision.
 alpha                 7.297352533e-3  The fine structure constant was
introduced to explain fine structure visible in spectral lines. It can be computed from mu0 c e^2 / 2 h with a loss of 3 digits precision and loss of precision in derived values which use alpha.
 bohrradius[?]            alpha / 4 pi Rinfinity
 prout[?]                 185.5 keV       nuclear binding energy equal to 1|12
binding energy of the deuteron
 Planck[?] constants

 planckmass[?]            2.1767e-8 kg    sqrt(hbar c / G)
 m_P[?]                   planckmass
 plancktime[?]            hbar / planckmass c^2
 t_P[?]                   plancktime
 plancklength[?]          plancktime c
 l_P[?]                   plancklength

 Masses of elementary particles

 electron          5.485799110e-4 u
 proton            1.00727646688 u
 neutron           1.00866491578 u
 muon              0.1134289168 u
 deuteron          2.01355321271 u
 alpha particle     4.0015061747 u

 particle wavelengths: the compton wavelength of a particle is
 defined as h / m c where m is the mass of the particle.

 Magnetic moments

 bohrmagneton[?]          e hbar / 2 electronmass
 mu_B[?]                  bohrmagneton
 nuclearmagneton[?]       e hbar / 2 protonmass
 mu_N[?]                  nuclearmagneton

 Units derived from physical constants

 kgf[?]                   kg force
 technicalatmosphere[?]   kgf / cm^2
 at                    technicalatmosphere
 hyl[?]                   kgf s^2 / m  Also gram-force s^2/m according to [15]
 mmHg[?]                  mm Hg
 torr                  mmHg    These units, both named after Evangelista
 tor                   Pa      Torricelli, should not be confused.
Acording to [15] the torr is actually atm/760 which is slightly different.
 inHg[?]                  inch Hg
 inH2O[?]                 inch water
 mmH2O[?]                 mm water
 eV                    e V     Energy acquired by a particle with charge e
 electronvolt          eV        when it is accelerated through 1 V
 lightyear             c julianyear  The 365.25 day year is specified in
NIST publication 811
 lightsecond[?]           c s
 lightminute[?]           c min
 parsec                au / tan(arcsec)   Unit of length equal to distance
 pc[?]                    parsec               from the sun to a point having
heliocentric parallax of 1 arcsec (derived from parallax second). A distant object with paralax theta will be about (arcsec/theta) parsecs from the sun (using the approximation that tan(theta) = theta).
 rydberg[?]               h c Rinfinity      Rydberg energy
 crith[?]                 0.089885 gram      The crith is the mass of one
liter of hydrogen at standard temperature and pressure.
 amagatvolume[?]          molarvolume
 amagat[?]                mol/amagatvolume   Used to measure gas densities
 lorentz[?]               bohrmagneton / h c  Used to measure the extent
 					       that the frequency of light
is shifted by a magnetic field.
 cminv[?]                 h c / cm           Unit of energy used in infrared
 invcm[?]                 cminv                spectroscopy.
 wavenumber            cminv
 kcal_mol[?]              kcal / mol N_A     kcal/mol is used as a unit of
energy by physical chemists.

 CGS system based on centimeter, gram and second

 dyne                  cm gram / s^2  force
 dyn[?]                   dyne
 erg                   cm dyne        energy
 poise[?]                 gram / cm s    viscosity, honors Jean Poiseuille
 P                     poise
 rhe[?]                   /poise         reciprocal viscosity
 stokes[?]                cm^2 / s       kinematic viscosity
 St[?]                    stokes
 stoke                 stokes
 lentor[?]                stokes         old name
 Gal[?]                   cm / s^2       acceleration, used in geophysics
 galileo               Gal            for earth's gravitational field
 					 (note that "gal" is for gallon
but "Gal" is the standard symbol for the gal which is evidently a shortened form of "galileo".)
 barye[?]                 dyne/cm^2      pressure
 barad[?]                 barye          old name
 kayser[?]                1/cm           Proposed as a unit for wavenumber
 balmer[?]                kayser         Even less common name than "kayser"
 kine[?]                  cm/s           velocity
 bole[?]                  g cm / s       momentum
 pond                  gram force
 glug[?]              gram force s^2 / cm  Mass which is accelerated at
1 cm/s^2 by 1 gram force
 darcy[?]         centipoise cm^2 / s atm  Measures permeability to fluid flow.

One darcy is the permeability of a medium that allows a flow of cc/s of a liquid of centipoise viscosity under a pressure gradient of atm/cm. Named for H. Darcy.

 mohm[?]                  cm / dyn s     mobile ohm, measure of mechanical
 mobileohm[?]             mohm             mobility
 mechanicalohm[?]         dyn s / cm     mechanical resistance
 acousticalohm[?]         dyn s / cm^5   ratio of the sound pressure of
1 dyn/cm^2 to a source of strength 1 cm^3/s
 ray                   acousticalohm
 rayl[?]                  dyn s / cm^3   Specific acoustical resistance
 eotvos[?]                1e-9 Gal/cm    Change in gravitational acceleration
over horizontal distance

 Electromagnetic units derived from the abampere

 abampere[?]              10 A           Current which produces a force of
 abamp[?]                 abampere         2 dyne/cm between two infinitely
 aA                    abampere         long wires that are 1 cm apart
 biot[?]                  aA             alternative name for abamp
 Bi                    biot
 abcoulomb[?]             abamp sec
 abcoul[?]                abcoulomb
 abfarad[?]               abampere sec / abvolt
 abhenry[?]               abvolt sec / abamp
 abvolt[?]                dyne cm / abamp sec
 abohm[?]                 abvolt / abamp
 abmho[?]                 /abohm
 gauss                 abvolt sec / cm^2
 Gs[?]                    gauss
 maxwell               abvolt sec     Also called the "line"
 Mx[?]                    maxwell
 oersted               gauss / mu0
 Oe                    oersted
 gilbert               gauss cm / mu0
 Gb                    gilbert
 Gi[?]                    gilbert
 unitpole[?]              4 pi maxwell
 emu                   erg/gauss  "electro-magnetic unit", a measure of
 				    magnetic moment, often used as emu/cm^3
to specify magnetic moment density.

 Gaussian system: electromagnetic units derived from statampere.

 Note that the Gaussian units are often used in such a way that Coulomb's law
 has the form F= q1 * q2 / r^2.  The constant 1|4*pi*epsilon0 is incorporated
 into the units.  From this, we can get the relation force=charge^2/dist^2.
 This means that the simplification esu^2 = dyne cm^2 can be used to simplify
 units in the Gaussian system, with the curious result that capacitance can be
 measured in cm, resistance in sec/cm, and inductance in sec^2/cm.  These
 units are given the names statfarad, statohm and stathenry below.

statampere[?] 10 A cm / s c statamp[?] statampere statvolt dyne cm / statamp sec statcoulomb statamp s esu statcoulomb statcoul[?] statcoulomb statfarad[?] statamp sec / statvolt cmcapacitance[?] statfarad stathenry[?] statvolt sec / statamp statohm[?] statvolt / statamp statmho[?] /statohm statmaxwell[?] statvolt sec franklin statcoulomb debye[?] 1e-18 statcoul cm unit of electrical dipole moment helmholtz[?] debye/angstrom^2 Dipole moment per area jar[?] 1000 statfarad approx capacitance of Leyden jar

 Some historical eletromagnetic units

intampere[?] 0.999835 A Defined as the current which in one intamp[?] intampere second deposits .001118 gram of silver from an aqueous solution of silver nitrate. intfarad[?] 0.999505 F intvolt[?] 1.00033 V intohm[?] 1.000495 ohm Defined as the resistance of a uniform column of mercury containing 14.4521 gram in a column 1.063 m long and maintained at 0 degC. daniell[?] 1.042 V Meant to be electromotive force of a Daniell cell, but in error by .04 V faraday[?] N_A e mol Charge that must flow to deposit or faraday_phys[?] 96521.9 C liberate one gram equivalent of any faraday_chem[?] 96495.7 C element. (The chemical and physical values are off slightly from what is obtained by multiplying by amu_chem or amu_phys. These values are from a 1991 NIST publication.) Note that there is a Faraday constant which is equal to N_A e and hence has units of C/mol. kappline[?] 6000 maxwell Named by and for Gisbert Kapp siemensunit[?] 0.9534 ohm Resistance of a meter long column of mercury with a 1 mm cross section.

 Photometric units

candle 1.02 candela Standard unit for luminous intensity hefnerunit[?] 0.9 candle in use before candela hefnercandle[?] hefnerunit violle[?] 20.17 cd luminous intensity of 1 cm^2 of platinum at its temperature of solidification (2045 K)

lumen cd sr Luminous flux (luminous energy per lm[?] lumen time unit)

talbot[?] lumen s Luminous energy lumberg[?] talbot

lux lm/m^2 Illuminance or exitance (luminous lx[?] lux flux incident on or coming from phot[?] lumen / cm^2 a surface) ph[?] phot footcandle[?] lumen/ft^2 Illuminance from a 1 candela source at a distance of one foot metercandle[?] lumen/m^2 Illuminance from a 1 candela source at a distance of one meter

mcs[?] metercandle s luminous energy per area, used to measure photographic exposure

nox 1e-3 lux These two units were proposed for skot[?] 1e-3 apostilb measurements relating to dark adapted eyes.

 Luminance measures

nit cd/m^2 Luminance: the intensity per projected stilb[?] cd / cm^2 area of an extended luminous source. sb[?] stilb (nit is from latin nitere = to shine.)

apostilb[?] cd/pi m^2 asb[?] apostilb blondel[?] apostilb Named after a French scientist.

 Equivalent luminance measures.  These units are units which measure
 the luminance of a surface with a specified exitance which obeys
 Lambert's law.  (Lambert's law specifies that luminous intensity of
 a perfectly diffuse luminous surface is proportional to the cosine
 of the angle at which you view the luminous surface.)

equivalentlux[?] cd / pi m^2 luminance of a 1 lux surface equivalentphot[?] cd / pi cm^2 luminance of a 1 phot surface lambert[?] cd / pi cm^2 footlambert[?] cd / pi ft^2

 The bril is used to express "brilliance" of a source of light on a
 logarithmic scale to correspond to subjective perception.  An increase of 1
 bril means doubling the luminance.  A luminance of 1 lambert is defined to
 have a brilliance of 1 bril.

bril[?] bril(x) [;lambert] 2^(x+-100) lamberts ;log2(bril/lambert)+100

 Some luminance data from the IES Lighting Handbook, 8th ed, 1993

sunlum[?] 1.6e9 cd/m^2 at zenith sunillum[?] 100e3 lux clear sky sunillum_o[?] 10e3 lux overcast sky sunlum_h[?] 6e6 cd/m^2 value at horizon skylum[?] 8000 cd/m^2 average, clear sky skylum_o[?] 2000 cd/m^2 average, overcast sky moonlum[?] 2500 cd/m^2

 Photographic Exposure Value

 The Additive Photographic EXposure (APEX) system developed in Germany in
 the 1960s was an attempt to simplify exposure determination for people
 who relied on exposure tables rather than exposure meters.  Shortly
 thereafter, nearly all cameras incorporated exposure meters, so the APEX
 system never caught on, but the concept of Exposure Value (EV) given by


     2^EV = --- = -- = --

     A = Relative aperture (f-number)
     T = Shutter time in seconds
     L = Scene luminance in cd/m2
     E = Scene illuminance in lux
     S = Arithmetic ISO film speed
     K = Reflected-light meter calibration constant
     C = Incident-light meter calibration constant

 remains in use.  Strictly speaking, an Exposure Value is a combination
 of aperture and shutter time, but it's also commonly used to indicate
 luminance (or illuminance).  Conversion to luminance or illuminance
 units depends on the ISO film speed and the meter calibration constant.
 Common practice is to use an ISO film speed of 100 (because film speeds
 are in even 1/3-step increments, the exact value is 64 * 2^(2|3)).
 Calibration constants vary among camera and meter manufacturers: Canon,
 Nikon, and Sekonic use a value of 12.5 for reflected-light meters, while
 Minolta and Pentax use a value of 14.  Minolta and Sekonic use a value
 of 250 for incident-light meters with flat receptors.

s100 64 * 2^(2|3) / lx s exact speed for ISO 100 film

 Reflected-light meter calibration constant with ISO 100 film

k1250[?] 12.5 (cd/m2) / lx s For Canon, Nikon, and Sekonic k1400[?] 14 (cd/m2) / lx s For Minolta and Pentax

 Incident-light meter calibration constant with ISO 100 film

c250[?] 250 lx / lx s flat-disc receptor

 Exposure value to scene luminance with ISO 100 film

 For Minolta or Pentax
ev100(x) [;cd/m^2] 2^x k1400 / s100; log2(ev100 s100 / k1400)
 For Canon, Nikon or Sekonic
ev100[?] ev100(x) [;cd/m^2] 2^x k1250 / s100; log2(ev100 s100 / k1250)

 Exposure value to scene illuminance with ISO 100 film

iv100[?] iv100(x) [1;lx] 2^x c250 / s100; log2(iv100 s100 / c250)

 Astronomical time measurements

 Astronmical time measurement is a complicated matter.  The rotation of the
 earth and motion of the planets is not uniform.  Originally the second was
 defined relative to the "mean solar day".  It is necessary to use the mean
 day because the earth's orbit is elliptical so the length of the day varies
 throughout the year.  Simon Newcomb discovered that there were significant
 irregularities in the rotation of the earth and he came up with equations
 using the location of a fictitious mean sun.  The length of the second was
 determined from the tropical year obtained from Newcomb's equations.  This
 second was officially used from 1960 to 1967, at which point atomic clocks
 replaced astronomical measurements for a standard of time.

 The measures that appear below are probably obtained from an "ephemeris"
 which is a set of equations that predicts the locations of the planets over

anomalisticyear[?] 365.2596 days The time between successive perihelion passages of the earth. siderealyear[?] 365.256360417 day The time for the earth to make one revolution around the sun relative to the stars. tropicalyear[?] 365.242198781 day The mean interval between vernal equinoxes. Differs from the sidereal year by 1 part in 26000 due to precession of the earth about its rotational axis combined with precession of the perihelion of the earth's orbit. gaussianyear[?] 365.2690 days The orbital period of a body in circular orbit at a distance of 1 au from the sun. Calculated from Kepler's third law. elipseyear[?] 346.62 days The line of nodes is the intersection of the plane of Earth's orbit around the sun with the plane of the moon's orbit around earth. Eclipses can only occur when the moon and sun are close to this line. The line rotates and appearances of the sun on the line of nodes occur every eclipse year. saros 223 synodicmonth The earth, moon and sun appear in the same arrangement every saros, so if an eclipse occurs, then one saros later, a similar eclipse will occur. (The saros is close to 19 eclipse years.) The eclipse will occur about 120 degrees west of the preceeding one because the saros is not an even number of days. After 3 saros, an eclipse will occur at approximately the same place. siderealday[?] 23.934469444 hour The sidereal day is the interval siderealhour[?] 1|24 siderealday between two successive transits siderealminute[?] 1|60 siderealhour of a star over the meridian, siderealsecond[?] 1|60 siderealminute or the time required for the earth to make one rotation relative to the stars. The more usual solar day is the time required to make a rotation relative to the sun. Because the earth moves in its orbit, it has to turn a bit extra to face the sun again, hence the solar day is slightly longer. anomalisticmonth[?] 27.55454977 day Time for the moon to travel from perigee to perigee nodicalmonth[?] 27.2122199 day The nodes are the points where draconicmonth[?] nodicalmonth an orbit crosses the ecliptic. draconiticmonth[?] nodicalmonth This is the time required to travel from the ascending node to the next ascending node. siderealmonth[?] 27.321661 day Time required for the moon to orbit the earth lunarmonth[?] 29 days+12 hours+44 minutes+2.8 seconds Time between full moons. Full synodicmonth[?] lunarmonth moon occur when the sun and lunation[?] synodicmonth moon are on opposite sides of lune[?] 1|30 lunation the earth. Since the earth lunour[?] 1|24 lune moves around the sun, the moon has to revolve a bit farther to get into the full moon configuration. year tropicalyear yr[?] year month 1|12 year mo month lustrum[?] 5 years The Lustrum was a Roman purification ceremony that took place every five years. Classically educated Englishmen used this term. decade 10 years century 100 years millennium 1000 years millennia millennium solaryear[?] year lunaryear[?] 12 lunarmonth calendaryear[?] 365 day commonyear[?] 365 day leapyear[?] 366 day julianyear[?] 365.25 day gregorianyear[?] 365.2425 day islamicyear[?] 354 day A year of 12 lunar months. They islamicleapyear[?] 355 day began counting on July 16, AD 622 when Muhammad emigrated to Medina (the year of the Hegira). They need 11 leap days in 30 years to stay in sync with the lunar year which is a bit longer than the 29.5 days of the average month. The months do not keep to the same seasons, but regress through the seasons every 32.5 years. islamicmonth[?] 1|12 islamicyear They have 29 day and 30 day months.

 The Hewbrew year is also based on lunar months, but synchronized to the solar
 calendar.  The months vary irregularly between 29 and 30 days in length, and
 the years likewise vary.  The regular year is 353, 354, or 355 days long.  To
 keep up with the solar calendar, a leap month of 30 days is inserted every
 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years of a 19 year cycle.  This
 gives leap years that last 383, 384, or 385 days.

 The Hartree system of atomic units, derived from fundamental units
 of mass (of electron), action (planck's constant), charge, and
 the coulomb constant.

 Fundamental units

atomicmass[?] electronmass atomiccharge[?] e atomicaction[?] hbar

 derived units (Warning: accuracy is lost from deriving them this way)

atomiclength[?] bohrradius atomictime[?] hbar^3/coulombconst^2 atomicmass e^4 Period of first bohr orbit atomicvelocity[?] atomiclength / atomictime atomicenergy[?] hbar / atomictime hartree[?] atomicenergy Hartree[?] hartree

 These thermal units treat entropy as charge, from [5]

thermalcoulomb[?] J/K entropy thermalampere[?] W/K entropy flow thermalfarad[?] J/K^2 thermalohm[?] K^2/W thermal resistance fourier thermalohm thermalhenry[?] J K^2/W^2 thermal inductance thermalvolt[?] K thermal potential difference

 United States units

 linear measure

 The US Metric Law of 1866 gave the exact relation 1 meter = 39.37 inches.
 From 1893 until 1959, the foot was exactly 1200|3937 meters.  In 1959
 the definition was changed to bring the US into agreement with other
 countries.  Since then, the foot has been exactly 0.3048 meters.  At the
 same time it was decided that any data expressed in feet derived from
 geodetic surveys within the US would continue to use the old definition.

US 1200|3937 m/ft These four values will convert US- US international measures to survey- US US Survey measures geodetic- US int[?] 3937|1200 ft/m Convert US Survey measures to int- int international measures

inch 2.54 cm in[?] inch foot 12 inch feet foot ft[?] foot yard 3 ft yd yard mile 5280 ft The mile was enlarged from 5000 ft to this number in order to make it an even number of furlongs. (The Roman mile is 5000 romanfeet.) line 1|12 inch Also defined as '.1 in' or as '1e-8 Wb' rod 5.5 USyard perch rod furlong 40 rod From "furrow long" statutemile[?] USmile league 3 USmile Intended to be an an hour's walk

 surveyor's measure

surveyorschain[?] 66 surveyft surveyorspole[?] 1|4 surveyorschain surveyorslink[?] 1|100 surveyorschain chain surveyorschain surveychain[?] chain ch[?] chain link surveyorslink acre 10 chain^2 intacre[?] 43560 ft^2 Acre based on international ft acrefoot[?] acre surveyfoot section[?] USmile^2 township 36 section homestead 160 acre Area of land granted by the 1862 Homestead Act of the United States Congress gunterschain[?] surveyorschain

engineerschain[?] 100 ft engineerslink[?] 1|100 engineerschain ramsdenschain[?] engineerschain ramsdenslink[?] engineerslink

 nautical measure

fathom 6 USft Originally defined as the distance from fingertip to fingertip with arms fully extended. nauticalmile[?] 1852 m Supposed to be one minute of latitude at the equator. That value is about 1855 m. Early estimates of the earth's circumference were a bit off. The value of 1852 m was made the international standard in 1929. The US did not accept this value until 1954. The UK switched in 1970.

cable 1|10 nauticalmile intcable[?] cable international cable cablelength cable UScable[?] 100 fathom navycablelength[?] 720 USft used for depth in water marineleague[?] 3 nauticalmile geographicalmile[?] brnauticalmile knot nauticalmile / hr click[?] km

 Avoirdupois weight

pound 0.45359237 kg The one normally used lb pound From the latin libra grain 1|7000 pound The grain is the same in all three weight systems. It was originally defined as the weight of a barley corn taken from the middle of the ear. ounce 1|16 pound oz ounce dram[?] 1|16 ounce dr[?] dram ushundredweight[?] 100 pounds cwt[?] hundredweight shorthundredweight[?] ushundredweight uston[?] shortton shortton[?] 2000 lb quarterweight[?] 1|4 uston shortquarterweight[?] 1|4 shortton shortquarter[?] shortquarterweight

 Troy Weight.  In 1828 the troy pound was made the first United States
 standard weight.  It was to be used to regulate coinage.

troypound[?] 5760 grain troyounce[?] 1|12 troypound ozt[?] troyounce pennyweight[?] 1|20 troyounce Abbreviated "d" in reference to a dwt[?] pennyweight Frankish coin called the "denier" minted in the late 700's. There were 240 deniers to the pound. assayton[?] mg ton / troyounce mg / assayton = troyounce / ton usassayton[?] mg uston / troyounce brassayton[?] mg brton / troyounce

 Some other jewelers units

metriccarat[?] 0.2 gram Defined in 1907 metricgrain[?] 50 mg carat metriccarat ct[?] carat jewelerspoint[?] 1|100 carat silversmithpoint[?] 1|4000 inch

 Apothecaries' weight

appound[?] troypound apounce[?] troyounce apdram[?] 1|8 apounce apscruple[?] 1|3 apdram

 Liquid measure

gal[?] gallon quart 1|4 gallon pint 1|2 quart gill 1|4 pint usgallon[?] 231 in^3 usquart[?] 1|4 usgallon uspint[?] 1|2 usquart usgill[?] 1|4 uspint usfluidounce[?] 1|16 uspint fluiddram[?] 1|8 usfloz minimvolume[?] 1|60 fluiddram qt quart pt[?] pint floz[?] fluidounce usfloz[?] usfluidounce fldr[?] fluiddram liquidbarrel[?] 31.5 usgallon usbeerbarrel[?] 2 beerkegs beerkeg[?] 15.5 usgallon Various among brewers

ponykeg[?] 1|2 beerkeg winekeg[?] 12 usgallon petroleumbarrel[?] 42 usgallon Originated in Pennsylvania oil barrel petroleumbarrel fields, from the winetierce bbl[?] barrel hogshead 2 liquidbarrel usfirkin[?] 9 gallon

 Dry measures: The Winchester Bushel was defined by William III in 1702 and
 legally adopted in the US in 1836.

usbushel[?] 2150.42 in^3 Volume of 8 inch cylinder with 18.5 bu[?] bushel inch diameter (rounded) peck 1|4 bushel uspeck[?] 1|4 usbushel brpeck[?] 1|4 brbushel pk[?] peck drygallon[?] 1|2 uspeck dryquart[?] 1|4 drygallon drypint[?] 1|2 dryquart drybarrel[?] 7056 in^3 Used in US for fruits, vegetables, and other dry commodities except for cranberries. cranberrybarrel[?] 5826 in^3 US cranberry barrel heapedbushel[?] 1.278 usbushel Why this particular value? Often rounded to 1.25 bushels.

 Grain measures.  The bushel as it is used by farmers in the USA is actually
 a measure of mass which varies for different commodities.  Canada uses the
 same bushel masses for most commodities, but not for oats.

wheatbushel[?] 60 lb soybeanbushel[?] 60 lb cornbushel[?] 56 lb ryebushel[?] 56 lb barleybushel[?] 48 lb oatbushel[?] 32 lb ricebushel[?] 45 lb canada_oatbushel[?] 34 lb

 Wine and Spirits measure

ponyvolume[?] 1 usfloz jigger 1.5 usfloz Can vary between 1 and 2 usfloz shot jigger Sometimes 1 usfloz eushot[?] 25 ml EU standard spirits measure fifth[?] 1|5 usgallon winebottle[?] 750 ml US industry standard, 1979 winesplit[?] 1|4 winebottle wineglass[?] 4 usfloz magnum[?] 1.5 liter Standardized in 1979, but given as 2 qt in some references metrictenth[?] 375 ml metricfifth[?] 750 ml metricquart[?] 1 liter

 French champagne bottle sizes

split 200 ml jeroboam 2 magnum rehoboam 3 magnum methuselah 4 magnum salmanazar[?] 6 magnum balthazar[?] 8 magnum nebuchadnezzar 10 magnum

 Water is "hard" if it contains various minerals, expecially calcium

clarkdegree[?] 1|70000 Content by weigh of calcium carbonate gpg[?] grains/gallon Divide by water's density to convert to a dimensionless concentration measure

 Shoe measures

shoeiron[?] 1|48 inch Used to measure leather in soles shoeounce[?] 1|64 inch Used to measure non-sole shoe leather

 USA shoe sizes.  These express the length of the shoe or the length
 of the "last", the form that the shoe is made on.

shoesize_delta[?] 1|3 inch USA shoe sizes differ by this amount shoe_men0[?] 8.25 inch shoe_women0[?] (7+11|12) inch shoe_boys0[?] (3+11|12) inch shoe_girls0[?] (3+7|12) inch

 European shoe size.  According to
      http://www.shoeline.com/footnotes/shoeterm.shtmlparis points

 sizes in Europe are measured with Paris points which simply measure
 the length of the shoe.

europeshoesize[?] 2|3 cm

 USA slang units

buck[?] US$ fin 5 US$ sawbuck[?] 10 US$ grand 1000 US$ greenback[?] US$ key kg usually of marijuana, 60's lid[?] 1 oz Another 60's weed unit footballfield[?] 100 yards marathon 26 miles + 385 yards


UK 1200000|3937014 m/ft The UK lengths were defined by british- UK a bronze bar manufactured in UK- UK 1844. Measurement of that bar revealed the dimensions given here.

brnauticalmile[?] 6080 ft Used until 1970 when the UK brknot[?] brnauticalmile / hr switched to the international brcable[?] 1|10 brnauticalmile nautical mile. admiraltymile[?] brnauticalmile admiraltyknot[?] brknot admiraltycable[?] brcable seamile[?] 6000 ft shackle[?] 15 fathoms Adopted 1949 by British navy

 British Imperial weight is mostly the same as US weight.  A few extra
 units are added here.

clove 7 lb stone 14 lb tod[?] 28 lb brquarterweight[?] 1|4 brhundredweight brhundredweight[?] 8 stone longhundredweight[?] brhundredweight longton[?] 20 brhundredweight brton[?] longton

 British Imperial volume measures

brminim[?] 1|60 brdram brscruple[?] 1|3 brdram fluidscruple[?] brscruple brdram[?] 1|8 brfloz brfluidounce[?] 1|20 brpint brfloz[?] brfluidounce brgill[?] 1|4 brpint brpint[?] 1|2 brquart brquart[?] 1|4 brgallon brgallon[?] 4.54609 l The British Imperial gallon was defined in 1824 to be the volume of water which weighed 10 pounds at 62 deg F with a pressure of 30 inHg. In 1963 it was defined to be the volume occupied by 10 pounds of distilled water of density 0.998859 g/ml weighed in air of density 0.001217 g/ml against weights of density 8.136 g/ml. This gives a value of approximately 4.5459645 liters, but the old liter was in force at this time. In 1976 the definition was changed to exactly 4.54609 liters using the new definition of the liter (1 dm^3). brbarrel[?] 36 brgallon Used for beer brbushel[?] 8 brgallon brheapedbushel[?] 1.278 brbushel brquarter[?] 8 brbushel brchaldron[?] 36 brbushel

 Units derived from imperial system

ouncedal[?] oz ft / s^2 force which accelerates an ounce at 1 ft/s^2 poundal[?] lb ft / s^2 same thing for a pound tondal[?] ton ft / s^2 and for a ton pdl[?] poundal psi pound force / inch^2 psia[?] psi absolute pressure tsi[?] ton force / inch^2 reyn[?] psi sec slug lbf s^2 / ft slugf[?] slug force slinch[?] lbf s^2 / inch Mass unit derived from inch second slinchf[?] slinch force pound-force system. Used in space applications where in/sec^2 was a natural acceleration measure. geepound[?] slug lbf lb force tonf[?] ton force lbm[?] lb kip[?] 1000 lbf from kilopound ksi[?] kip / in^2 mil 0.001 inch thou 0.001 inch circularinch[?] 1|4 pi in^2 area of a one-inch diameter circle circularmil[?] 1|4 pi mil^2 area of one-mil diameter circle cmil[?] circularmil cental[?] 100 pound centner[?] cental caliber 0.01 inch for measuring bullets duty ft lbf celo[?] ft / s^2 jerk ft / s^3 australiapoint[?] 0.01 inch The "point" is used to measure rainfall in Australia sabin[?] ft^2 Measure of sound absorption equal to the absorbing power of one square foot of a perfectly absorbing material. The sound absorptivity of an object is the area times a dimensionless absorptivity coefficient. standardgauge[?] 4 ft + 8.5 in Standard width between railroad track flag 5 ft^2 Construction term referring to sidewalk. rollwallpaper[?] 30 ft^2 Area of roll of wall paper fillpower[?] in^3 / ounce Density of down at standard pressure. The best down has 750-800 fillpower. pinlength[?] 1|16 inch A 17 pin is 17/16 in long in the USA. buttonline[?] 1|40 inch The line was used in 19th century USA to measure width of buttons. scoopnumber[?] /quart Ice cream scoops are labeled with a number specifying how many scoops fill a quart. beespace[?] 1|4 inch Bees will fill any space that is smaller than the bee space and leave open spaces that are larger. The size of the space varies with species. diamond 8|5 ft Marking on US tape measures that is useful to carpenters who wish to place five studs in an 8 ft distance. Note that the numbers appear in red every 16 inches as well, giving six divisions in 8 feet. retmaunit[?] 1.75 in Height of rack mountable equipment. U retmaunit Equipment should be 1|32 inch narrower than its U measurement indicates to allow for clearance, so 4U=(6+31|32)in

 Other units of work, energy, power, etc

 Calories: energy to raise a gram of water one degree celsius

cal_IT[?] 4.1868 J International Table calorie cal_th[?] 4.184 J Thermochemical calorie cal_fifteen[?] 4.18580 J Energy to go from 14.5 to 15.5 degC cal_twenty[?] 4.18190 J Energy to go from 19.5 to 20.5 degC cal_mean[?] 4.19002 J 1|100 energy to go from 0 to 100 degC calorie cal_IT cal calorie calorie_IT[?] cal_IT thermcalorie[?] cal_th calorie_th[?] thermcalorie Calorie kilocalorie the food Calorie thermie[?] 1e6 cal_fifteen Heat required to raise the temperature of a tonne of water from 14.5 to 15.5 degC.

 btu definitions: energy to raise a pound of water 1 degF

btu[?] cal lb degF / gram K international table BTU britishthermalunit[?] btu btu_IT[?] btu btu_th[?] cal_th lb degF / gram K btu_mean[?] cal_mean lb degF / gram K quad[?] quadrillion btu

ECtherm[?] 1.05506e8 J Exact definition, close to 1e5 btu UStherm[?] 1.054804e8 J Exact definition therm[?] UStherm toe 1e10 cal_IT ton oil equivalent. Energy released by burning one metric ton of oil. [18] tonscoal[?] 1|2.3 toe Energy in metric ton coal from [18]. naturalgas[?] toe / 1270 m^3 Energy released from natural gas from [18]. (At what pressure?)

 Celsius heat unit: energy to raise a pound of water 1 degC

celsiusheatunit[?] cal lb degC / gram K chu[?] celsiusheatunit

 The horsepower is supposedly the power of one horse pulling.   Obviously
 different people had different horses.

ushorsepower[?] 550 foot pound force / sec Invented by James Watt hp[?] horsepower metrichorsepower[?] 75 kilogram force meter / sec electrichorsepower[?] 746 W boilerhorsepower[?] 9809.50 W waterhorsepower[?] 746.043 W brhorsepower[?] 745.70 W donkeypower[?] 250 W

 Thermal insulance: Thermal conductivity has dimension power per area per
 (temperature difference per length thickness) which comes out to W / K m.  If
 the thickness is fixed, then the conductance will have units of W / K m^2.
 Thermal insulance is the reciprocal.

Rvalue[?] degF ft^2 hr / btu Uvalue[?] 1/Rvalue europeanUvalue[?] watt / m^2 K RSI degC m^2 / W clo[?] 0.155 degC m^2 / W Supposed to be the insulance required to keep a resting person comfortable indoors. The value given is from NIST and the CRC, but [5] gives a slightly different value of 0.875 ft^2 degF hr / btu. tog[?] 0.1 degC m^2 / W Also used for clothing.

 Misc other measures

ENTROPY ENERGY / TEMPERATURE clausius[?] 1e3 cal/K A unit of physical entropy langley thermcalorie/cm^2 Used in radiation theory poncelet[?] 100 kg force m / s tonrefrigeration[?] ton 144 btu / lb day One ton refrigeration is the rate of heat extraction required turn one ton of water to ice in a day. Ice is defined to have a latent heat of 144 btu/lb. tonref[?] tonrefrigeration refrigeration tonref / ton frigorie[?] 1000 cal_fifteen Used in refrigeration engineering. tnt[?] 1e9 cal_th / ton So you can write tons-tnt. This is a defined, not measured, value. airwatt[?] 8.5 (ft^3/min) inH2O Measure of vacuum power as pressure times air flow.

 Permeability: The permeability or permeance, n, of a substance determines
 how fast vapor flows through the substance.  The formula W = n A dP
 holds where W is the rate of flow (in mass/time), n is the permeability,
 A is the area of the flow path, and dP is the vapor pressure difference.

perm_0C[?] grain / hr ft^2 inHg perm_zero[?] perm_0C perm_0[?] perm_0C perm[?] perm_0C perm_23C[?] grain / hr ft^2 in Hg23C perm_twentythree[?] perm_23C

 Counting measures

pair[?] 2 brace[?] 2 nest 3 often used for items like bowls that nest together hattrick[?] 3 Used in sports, especially cricket and ice hockey to report the number of goals. dicker[?] 10 dozen 12 bakersdozen[?] 13 score 20 flock[?] 40 timer[?] 40 shock 60 gross 144 greatgross[?] 12 gross tithe 1|10 From Anglo-Saxon word for tenth

 Paper counting measure

shortquire[?] 24 quire[?] 25 shortream[?] 480 ream[?] 500 perfectream[?] 516 bundle[?] 2 reams bale[?] 5 bundles

 Paper measures

pointthickness[?] mil

 The metric paper sizes are defined so that if a sheet is cut in half
 along the short direction, the result is two sheets which are
 similar to the original sheet.  This means that for any metric size,
 the long side is close to sqrt(2) times the length of the short
 side.  Each series of sizes is generated by repeated cuts in half,
 with the values rounded down to the nearest millimeter.

A6paper[?] 105 mm 148 mm A7paper[?] 74 mm 105 mm A8paper[?] 52 mm 74 mm A9paper[?] 37 mm 52 mm A10paper[?] 26 mm 37 mm

B0paper[?] 1000 mm 1414 mm The basic B size has an area B1paper[?] 707 mm 1000 mm of sqrt(2) square meters. B2paper[?] 500 mm 707 mm B3paper[?] 353 mm 500 mm B4paper[?] 250 mm 353 mm B5paper[?] 176 mm 250 mm B6paper[?] 125 mm 176 mm B7paper[?] 88 mm 125 mm B8paper[?] 62 mm 88 mm B9paper[?] 44 mm 62 mm B10paper[?] 31 mm 44 mm

C0paper[?] 917 mm 1297 mm The basic C size has an area C1paper[?] 648 mm 917 mm of sqrt(sqrt(2)) square meters. C2paper[?] 458 mm 648 mm C3paper[?] 324 mm 458 mm Intended for envelope sizes C4paper[?] 229 mm 324 mm C5paper[?] 162 mm 229 mm C6paper[?] 114 mm 162 mm C7paper[?] 81 mm 114 mm C8paper[?] 57 mm 81 mm C9paper[?] 40 mm 57 mm C10paper[?] 28 mm 40 mm

 gsm (Grams per Square Meter), a sane, metric paper weight measure

gsm[?] grams / meter^2

 In the USA, a collection of crazy historical paper measures are used.  Paper
 is measured as a weight of a ream of that particular type of paper.  This is
 sometimes called the "substance" or "basis" (as in "substance 20" paper).
 The standard sheet size or "basis size" varies depending on the type of
 paper.  As a result, 20 pound bond paper and 50 pound text paper are actually
 about the same weight.  The different sheet sizes were historically the most
 convenient for printing or folding in the different applications.  These
 different basis weights are standards maintained by American Society for
 Testing Materials (ASTM) and the American Forest and Paper Association

poundbookpaper[?] lb / 25 inch 38 inch ream lbbook[?] poundbookpaper poundtextpaper[?] poundbookpaper lbtext[?] poundtextpaper poundoffsetpaper[?] poundbookpaper For offset printing lboffset[?] poundoffsetpaper poundbiblepaper[?] poundbookpaper Designed to be lightweight, thin, lbbible[?] poundbiblepaper strong and opaque. poundtagpaper[?] lb / 24 inch 36 inch ream lbtag[?] poundtagpaper poundbagpaper[?] poundtagpaper lbbag[?] poundbagpaper poundnewsprintpaper[?] poundtagpaper lbnewsprint[?] poundnewsprintpaper poundposterpaper[?] poundtagpaper lbposter[?] poundposterpaper poundtissuepaper[?] poundtagpaper lbtissue[?] poundtissuepaper poundwrappingpaper[?] poundtagpaper lbwrapping[?] poundwrappingpaper poundwaxingpaper[?] poundtagpaper lbwaxing[?] poundwaxingpaper poundglassinepaper[?] poundtagpaper lbglassine[?] poundglassinepaper poundcoverpaper[?] lb / 20 inch 26 inch ream lbcover[?] poundcoverpaper poundindexpaper[?] lb / 25.5 inch 30.5 inch ream lbindex[?] poundindexpaper poundbondpaper[?] lb / 17 inch 22 inch ream Bond paper is stiff and lbbond[?] poundbondpaper durable for repeated poundwritingpaper[?] poundbondpaper filing, and it resists lbwriting[?] poundwritingpaper ink penetration. poundledgerpaper[?] poundbondpaper lbledger[?] poundledgerpaper poundcopypaper[?] poundbondpaper lbcopy[?] poundcopypaper poundblottingpaper[?] lb / 19 inch 24 inch ream lbblotting[?] poundblottingpaper poundblankspaper[?] lb / 22 inch 28 inch ream lbblanks[?] poundblankspaper poundpostcardpaper[?] lb / 22.5 inch 28.5 inch ream lbpostcard[?] poundpostcardpaper poundweddingbristol[?] poundpostcardpaper lbweddingbristol[?] poundweddingbristol poundbristolpaper[?] poundweddingbristol lbbristol[?] poundbristolpaper poundboxboard[?] lb / 1000 ft^2 lbboxboard[?] poundboxboard poundpaperboard[?] poundboxboard lbpaperboard[?] poundpaperboard

 When paper is marked in units of M, it means the weight of 1000 sheets of the
 given size of paper.  To convert this to paper weight, divide by the size of
 the paper in question.

paperM[?] lb / 1000


fournierpoint[?] 0.1648 inch / 12 First definition of the printers point made by Pierre Fournier who defined it in 1737 as 1|12 of a cicero which was 0.1648 inches. olddidotpoint[?] 1|72 frenchinch François Ambroise Didot, one of a family of printers, changed Fournier's definition around 1770 to fit to the French units then in use. bertholdpoint[?] 1|2660 m H. Berthold tried to create a metric version of the didot point in 1878. INpoint[?] 0.4 mm This point was created by a group directed by Fermin Didot in 1881 and is associated with the imprimerie nationale. It doesn't seem to have been used much. germandidotpoint[?] 0.376065 mm Exact definition appears in DIN 16507, a German standards document of 1954. Adopted more broadly in 1966 by ??? metricpoint[?] 3|8 mm Proposed in 1977 by Eurograf point 1|72.27 inch The American point was invented printerspoint[?] point by Nelson Hawks in 1879 and dominates USA publishing. It was standardized by the American Typefounders Association at the value of 0.013837 inches exactly. Knuth uses the approximation given here (which is very close). The comp.fonts FAQ claims that this value is supposed to be 1|12 of a pica where 83 picas is equal to 35 cm. But this value differs from the standard. texscaledpoint[?] 1|65536 point The TeX typesetting system uses texsp[?] texscaledpoint this for all computations. computerpoint[?] 1|72 inch The American point was rounded computerpica[?] 12 computerpoint to an even 1|72 inch by computer postscriptpoint[?] computerpoint people at some point. pspoint[?] postscriptpoint Q 1|4 mm Used in Japanese phototypesetting Q is for quarter frenchprinterspoint[?] olddidotpoint didotpoint[?] germandidotpoint This seems to be the dominant value europeanpoint[?] didotpoint for the point used in Europe cicero 12 didotpoint

stick[?] 2 inches

 Type sizes

excelsior 3 point brilliant[?] 3.5 point diamondtype[?] 4 point pearl 5 point agate 5.5 point Originally agate type was 14 lines per inch, giving a value of 1|14 in. ruby agate British nonpareil[?] 6 point mignonette[?] 6.5 point emerald mignonette British minion[?] 7 point brevier[?] 8 point bourgeois 9 point longprimer[?] 10 point smallpica[?] 11 point pica 12 point english 14 point columbian 16 point greatprimer[?] 18 point paragon[?] 20 point meridian 44 point canon 48 point

 German type sizes

nonplusultra[?] 2 didotpoint brillant[?] 3 didotpoint diamant 4 didotpoint perl 5 didotpoint nonpareille[?] 6 didotpoint kolonel[?] 7 didotpoint petit[?] 8 didotpoint borgis[?] 9 didotpoint korpus[?] 10 didotpoint corpus korpus garamond korpus mittel[?] 14 didotpoint tertia[?] 16 didotpoint text 18 didotpoint kleine_kanon[?] 32 didotpoint kanon[?] 36 didotpoint grobe_kanon[?] 42 didotpoint missal[?] 48 didotpoint kleine_sabon[?] 72 didotpoint grobe_sabon[?] 84 didotpoint

 Information theory units.  Note that the name "entropy" is used both
 to measure information and as a physical quantity.

nat[?] ln(2) bits Entropy measured base e

hartley[?] log2(10) bits Entropy of a uniformly distributed random variable over 10 symbols.


bps bit/sec Sometimes the term "baud" is incorrectly used to refer to bits per second. Baud refers to symbols per second. Modern modems transmit several bits per symbol. byte 8 bit Not all machines had 8 bit B byte bytes, but these days most of them do. But beware: for transmission over modems, a few extra bits are used so there are actually 10 bits per byte. nybble[?] 4 bits Half of a byte. Sometimes equal to different lengths such as 3 bits. nibble nybble meg megabyte Some people consider these units along with the kilobyte gig[?] gigabyte to be defined according to powers of 2 with the kilobyte equal to 2^10 bytes, the megabyte equal to 2^20 bytes and the gigabyte equal to 2^30 bytes but these usages are forbidden by SI. Binary prefixes have been defined by IEC to replace the SI prefixes. Use them to get the binary values: KiB, MiB, and GiB. jiffy 0.01 sec This is defined in the Jargon File jiffies[?] jiffy (http://www.jargon.org) as being the duration of a clock tick for measuring wall-clock time. Supposedly the value used to be 1|60 sec or 1|50 sec depending on the frequency of AC power, but then 1|100 sec became more common. On linux systems, this term is used and for the Intel based chips, it does have the value of .01 sec. The Jargon File also lists two other definitions: millisecond, and the time taken for light to travel one foot.

 Musical measures.  Musical intervals expressed as ratios.  Multiply
 two intervals together to get the sum of the interval.  The function
 musicalcent can be used to convert ratios to cents.

 Perfect intervals

octave 2 majorsecond[?] musicalfifth^2 / octave majorthird[?] 5|4 minorthird[?] 6|5 musicalfourth[?] 4|3 musicalfifth[?] 3|2 majorsixth[?] musicalfourth majorthird minorsixth[?] musicalfourth minorthird majorseventh[?] musicalfifth majorthird minorseventh[?] musicalfifth minorthird

pythagoreanthird[?] majorsecond musicalfifth^2 / octave syntoniccomma[?] pythagoreanthird / majorthird pythagoreancomma[?] musicalfifth^12 / octave^7

 Equal tempered definitions

semitone octave^(1|12) musicalcent[?] (x) [1;1] semitone^(x/100) ; 100 log(musicalcent)/log(semitone)

 Musical note lengths.

wholenote[?] ! halfnote[?] 1|2 wholenote quarternote[?] 1|4 wholenote eighthnote[?] 1|8 wholenote sixteenthnote[?] 1|16 wholenote thirtysecondnote[?] 1|32 wholenote sixtyfourthnote[?] 1|64 wholenote dotted[?] 3|2 doubledotted[?] 7|4 breve doublewholenote semibreve wholenote minimnote[?] halfnote crochet quarternote quaver eighthnote semiquaver sixteenthnote demisemiquaver[?] thirtysecondnote hemidemisemiquaver[?] sixtyfourthnote semidemisemiquaver[?] hemidemisemiquaver

 yarn and cloth measures

 yarn linear density

woolyarnrun[?] 1600 yard/pound 1600 yds of "number 1 yarn" weighs a pound. yarncut[?] 300 yard/pound Less common system used in Pennsylvania for wool yarn cottonyarncount[?] 840 yard/pound linenyarncount[?] 300 yard/pound Also used for hemp and ramie worstedyarncount[?] 1680 ft/pound metricyarncount[?] meter/gram denier[?] 1|9 tex used for silk and rayon manchesteryarnnumber[?] drams/1000 yards old system used for silk pli[?] lb/in typp[?] 1000 yd/lb asbestoscut[?] 100 yd/lb used for glass and asbestos yarn

tex gram / km rational metric yarn measure, meant drex[?] 0.1 tex to be used for any kind of yarn poumar[?] lb / 1e6 yard

 yarn and cloth length

skeincotton[?] 80*54 inch 80 turns of thread on a reel with a 54 in circumference (varies for other kinds of thread) cottonbolt[?] 120 ft cloth measurement woolbolt[?] 210 ft

bolt cottonbolt heer[?] 600 yards cut[?] 300 yards used for wet-spun linen yarn lea 300 yards

 drug dosage

mcg[?] microgram Frequently used for vitamins iudiptheria[?] 62.8 microgram IU is for international unit iupenicillin[?] 0.6 microgram iuinsulin[?] 41.67 microgram drop 1|20 ml The drop was an old "unit" that was replaced by the minim. But I was told by a pharmacist that in his profession, the conversion of 20 drops per ml is actually used. bloodunit[?] 450 ml For whole blood. For blood components, a blood unit is the quanity of the component found in a blood unit of whole blood. The human body contains about 12 blood units of whole blood.

 fixup units for times when prefix handling doesn't do the job

hectare hectoare megohm[?] megaohm kilohm[?] kiloohm microhm[?] microohm megalerg[?] megaerg 'L' added to make it pronounceable [18].

 Exchange rates from the New York Times, 27 July 1999

 Some European currencies have permanent fixed exchange rates with
 the Euro.  These rates were taken from the EC's web site:

[[$]] dollar mark germanymark bolivar venezuelabolivar peseta spainpeseta rand southafricarand escudo[?] portugalescudo sol perunewsol guilder netherlandsguilder hollandguilder[?] netherlandsguilder peso mexicopeso yen japanyen lira italylira rupee indiarupee drachma greecedrachma franc francefranc markka finlandmarkka sucre ecuadorsucre poundsterling[?] britainpound

 ISO currency codes

AED[?] unitedarabdirham ATS[?] austriaschilling AUD australiadollar BEF[?] belgiumfranc

BRR[?] brazilreal CAD canadadollar CHF[?] switzerlandfranc CLP[?] chilepeso COP[?] colombiapeso CZK[?] czechkoruna DEM[?] germanymark DKK[?] denmarkkrone ECS ecuadorsucre EGP[?] egyptpound ESP spainpeseta EUR euro FIM[?] finlandmarkka FRF[?] francefranc GBP britainpound GRD greecedrachma HKD[?] hongkongdollar HUF[?] hungaryforint IDR[?] indonesiarupiah IEP[?] irelandpunt ILS israelshekel IND[?] indiarupee ITL[?] italylira JOD[?] jordandinar JPY japanyen KRW[?] southkoreawon LBP[?] lebanonpound LUF[?] luxemburgfranc MYR[?] malaysiaringgit MXP[?] mexicopeso NLG[?] netherlandsguilder NOK norwaykrone NZD newzealanddollar PEN[?] perunewsol PHP philippinespeso PLZ[?] polandzloty PTE[?] portugalescudo RUR[?] russiaruble SAR saudiarabiariyal SEK swedenkrona SGD[?] singaporedollar SKK[?] slovakiakoruna THB thailandbaht TRL turkeylira TWD[?] taiwandollar USD US$ VEB venezuelabolivar XEU[?] euro ZAR[?] southafricarand

UKP GBP Not an ISO code, but looks like one, and sometimes used on usenet.

 Money on the gold standard, used in the late 19th century and early
 20th century.

olddollargold[?] 23.22 grains goldprice Used until 1934 newdollargold[?] 96|7 grains goldprice After Jan 31, 1934 dollargold[?] newdollargold poundgold[?] 113 grains goldprice

 Nominal masses of US coins.  Note that dimes, quarters and half dollars
 have weight proportional to value.  Before 1965 it was $40 / kg.

USpennyweight[?] 2.5 grams Since 1982, 48 grains before USnickelweight[?] 5 grams USdimeweight[?] 10 cents / (20 US$ / lb) Since 1965 USquarterweight[?] 25 cents / (20 US$ / lb) Since 1965 UShalfdollarweight[?] 50 cents / (20 US$ / lb) Since 1971 USdollarmass[?] 8.1 grams

 British currency

quid britainpound Slang names fiver 5 quid tenner[?] 10 quid

shilling 1|20 britainpound Before decimalisation, there oldpence[?] 1|12 shilling were 20 shillings to a pound, farthing 1|4 oldpence each of twelve old pence crown 5 shilling brpenny[?] 0.01 britainpound pence penny tuppence[?] 2 pence tuppenny[?] tuppence oldpenny[?] oldpence oldtuppence[?] 2 oldpence oldtuppenny[?] oldtuppence threepence[?] 3 oldpence threepence never refers to new money threepenny[?] threepence oldthreepence[?] threepence oldthreepenny[?] threepence oldhalfpenny[?] halfoldpenny oldhapenny[?] oldha'penny brpony[?] 25 britainpound

 Canadian currency

loony 1 canadadollar This coin depicts a loon toony[?] 2 canadadollar

 Oceanographic flow

sverdrup 1e6 m^3 / sec Used to express flow of ocean currents. Named after Norwegian oceanographer H. Sverdrup.

 In vacuum science and some other applications, gas flow is measured
 as the product of volumetric flow and pressure.  This is useful
 because it makes it easy to compare with the flow at standard
 pressure (one atmosphere).  It also directly relates to the number
 of gas molecules per unit time, and hence to the mass flow if the
 molecular mass is known.

sccm[?] atm cc/min 's' is for "standard" to indicate sccs[?] atm cc/sec flow at standard pressure scfh[?] atm ft^3/hour scfm[?] atm ft^3/min slpm[?] atm liter/min slph[?] atm liter/hour lusec[?] liter micron Hg / s Used in vacuum science

 Wire Gauge

 This area is a nightmare with huge charts of wire gauge diameters
 that usually have no clear origin.  There are at least 5 competing wire gauge
 systems to add to the confusion.  The use of wire gauge is related to the
 manufacturing method: a metal rod is heated and drawn through a hole.  The
 size change can't be too big.  To get smaller wires, the process is repeated
 with a series of smaller holes.  Generally larger gauges mean smaller wires.
 The gauges often have values such as "00" and "000" which are larger sizes
 than simply "0" gauge.  In the tables that appear below, these gauges must be
 specified as negative numbers (e.g. "00" is -1, "000" is -2, etc).
 Alternatively, you can use the following units:

g00[?] (-1) g000[?] (-2) g0000[?] (-3) g00000[?] (-4) g000000[?] (-5) g0000000[?] (-6)

 American Wire Gauge (AWG) or Brown & Sharpe Gauge appears to be the most
 important gauge. ASTM B-258 specifies that this gauge is based on geometric
 interpolation between gauge 0000, which is 0.46 inches exactly, and gauge 36
 which is 0.005 inches exactly.  Therefore, the diameter in inches of a wire
 is given by the formula 1|200 92^((36-g)/39).  Note that 92^(1/39) is close
 to 2^(1/6), so diameter is approximately halved for every 6 gauges.  For the
 repeated zero values, use negative numbers in the formula.  The same document
 also specifies rounding rules which seem to be ignored by makers of tables.
 Gauges up to 44 are to be specified with up to 4 significant figures, but no
 closer than 0.0001 inch.  Gauges from 44 to 56 are to be rounded to the
 nearest 0.00001 inch.

 In addition to being used to measure wire thickness, this gauge is used to
 measure the thickness of sheets of aluminum, copper, and most metals other
 than steel, iron and zinc.

wiregauge(g) [;m] 1|200 92^((36+(-g))/39) in;36+(-39)ln(200 wiregauge/in)/ln(92)

 Next we have the SWG, the Imperial or British Standard Wire Gauge.  This one
 is piecewise linear.  It was used for aluminum sheets.

 The following is from the Appendix to ASTM B 258

    For example, in U.S. gage, the standard for sheet metal is based on the
    weight of the metal, not on the thickness. 16-gage is listed as
    approximately .0625 inch thick and 40 ounces per square foot (the original
    standard was based on wrought iron at .2778 pounds per cubic inch; steel
    has almost entirely superseded wrought iron for sheet use, at .2833 pounds
    per cubic inch). Smaller numbers refer to greater thickness. There is no
    formula for converting gage to thickness or weight.

 It's rather unclear from the passage above whether the plate gauge values are
 therefore wrong if steel is being used.  Reference [15] states that steel is
 in fact measured using this gauge (under the name Manufacturers' Standard
 Gauge) with a density of 501.84 lb/ft3 = 0.2904 lb/in3 used for steel.
 But this doesn't seem to be the correct density of steel (.2833 lb/in3 is

 This gauge was established in 1893 for purposes of taxation.

 Old plate gauge for iron

 Manufacturers Standard Gage

 A special gauge is used for zinc sheet metal.  Notice that larger gauges
 indicate thicker sheets.

 Screw sizes

 In the USA, screw diameters are reported using a gauge number.
 Metric screws are reported as Mxx where xx is the diameter in mm.

 Ring size. All ring sizes are given as the circumference of the ring.

 USA ring sizes.  Several slightly different definitions seem to be in
 circulation.  According to [15], the interior diameter of size n ring in
 inches is 0.32 n + 0.458 for n ranging from 3 to 13.5 by steps of 0.5.  The
 size 2 ring is inconsistently 0.538in and no 2.5 size is listed.

 However, other sources list 0.455 + 0.0326 n and 0.4525 + 0.0324 n as the
 diameter and list no special case for size 2.  (Or alternatively they are
 1.43 + .102 n and 1.4216+.1018 n for measuring circumference in inches.)  One
 reference claimed that the original system was that each size was 1|10 inch
 circumference, but that source doesn't have an explanation for the modern
 system which is somewhat different.

 Old practice in the UK measured rings using the "Wheatsheaf gauge" with sizes
 specified alphabetically and based on the ring inside diameter in steps of
 1|64 inch.  This system was replaced in 1987 by British Standard 6820 which
 specifies sizes based on circumference.  Each size is 1.25 mm different from
 the preceding size.  The baseline is size C which is 40 mm circumference.
 The new sizes are close to the old ones.  Sometimes it's necessary to go
 beyond size Z to Z+1, Z+2, etc.

 Japanese sizes start with size 1 at a 13mm inside diameter and each size is
 1|3 mm larger in diameter than the previous one.  They are multiplied by pi
 to give circumference.

 The European ring sizes are the length of the circumference in mm minus 40.


mph mile/hr mpg[?] mile/gal kph[?] km/hr fL footlambert fpm[?] ft/min fps ft/s rpm rev/min rps[?] rev/sec mi[?] mile mbh[?] 1e3 btu/hour mcm[?] 1e3 circularmil ipy[?] inch/year used for corrosion rates ccf[?] 100 ft^3 used for selling water [18] Mcf[?] 1000 ft^3 not million cubic feet [18] kp[?] kilopond kpm[?] kp meter kWh kW hour hph[?] hp hour

 Radioactivity units

becquerel /s Activity of radioactive source Bq[?] becquerel curie 3.7e10 Bq Defined in 1910 as the radioactivity Ci[?] curie emitted by the amount of radon that is in equilibrium with 1 gram of radium. rutherford[?] 1e6 Bq

gray J/kg Absorbed dose of radiation Gy[?] gray rad 1e-2 Gy From Radiation Absorbed Dose rep[?] 8.38 mGy Roentgen Equivalent Physical, the amount of radiation which , absorbed in the body, would liberate the same amount of energy as 1 roentgen of X rays would, or 97 ergs.

sievert J/kg Dose equivalent: dosage that has the Sv sievert same effect on human tissues as 200 rem 1e-2 Sv keV X-rays. Different types of radiation are weighted by the Relative Biological Effectiveness (RBE).

Radiation type RBE X-ray, gamma ray 1 beta rays, > 1 MeV 1 beta rays, < 1 MeV 1.08 neutrons, < 1 MeV 4-5 neutrons, 1-10 MeV 10 protons, 1 MeV 8.5 protons, .1 MeV 10 alpha, 5 MeV 15 alpha, 1 MeV 20

The energies are the kinetic energy of the particles. Slower particles interact more, so they are more effective ionizers, and hence have higher RBE values.

rem stands for Roentgen Equivalent Mammal

roentgen 2.58e-4 C / kg Ionizing radiation that produces 1 statcoulomb of charge in 1 cc of dry air at stp. rontgen roentgen Sometimes it appears spelled this way sievertunit[?] 8.38 rontgen Unit of gamma ray dose delivered in one hour at a distance of 1 cm from a point source of 1 mg of radium enclosed in platinum .5 mm thick.

eman[?] 1e-7 Ci/m^3 radioactive concentration mache[?] 3.7e-7 Ci/m^3

 A few German units as currently in use.

zentner[?] 50 kg doppelzentner[?] 2 zentner pfund[?] 500 g

 Some definitions using ISO 8859-1 characters

¢ cent £ britainpound ¥ japanyen ångström angstrom Å angstrom röntgen roentgen

 The following units were in the unix units database but do not appear in
 this file:

    wey[?]      used for cheese, salt and other goods.  Measured mass or
    waymass[?]  volume depending on what was measured and where the measuring
took place. A wey of cheese ranged from 200 to 324 pounds.

    sack     No precise definition

    spindle[?]  The length depends on the type of yarn

    block    Defined variously on different computer systems

    erlang   A unit of telephone traffic defined variously.
Omitted because there are no other units for this dimension. Is this true? What about CCS = 1/36 erlang? Erlang is supposed to be dimensionless. One erlang means a single channel occupied for one hour.

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