Like the bel it is a logarithmic measure; the difference being that where the bel uses base 10 logarithm to compute ratios, the neper uses base e (2.71828182846...). The value in nepers, Np , is given by Np = ln(x _{1}/x _{2}), where x _{1} and x _{2} are the values of interest, and ln is the natural logarithm, i.e., logarithm to the base e.
The neper is often used to express voltage and current ratios, whereas the decibel is usually used to express power ratios. Taking that into account we have
Like the dB, the Np is a dimensionless unit[?]. The ITU recognizes both units.
Source: from Federal Standard 1037C and from MILSTD188
In Egyptian mythology, Neper was a god of grain, especially barley and emmer wheat. His female counterpart was Nepit.
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