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Duodecimal, sometimes called dozenal, is a base 12 number system.

The Dozenal Society of America and Dozenal Society of Great Britain promote that a base 12 system is better than the decimal system mathematically and in many other ways. Since 2, 3, 4, 6 are factors of 12, it is a convenient number in doing fractions. Compared to factor 2 and 5 in the decimal system, duodecimal seems to be more versatile.

Base 12 number system is not common, but at least one example of duodecimal numerals is in use in the Chepang language of Nepal.

Historically, the number 12 was used in many civilizations. It is believed that the observation of 12 appearances of the Moon in a year is the reason why this number is used universally regardless of culture. Example of such usage include 12 months in a year, 12 hours on a clock, 12 traditional time divisions in a Chinese day, 12 signs of the zodiac in horoscope, 12 animal signs in Chinese astrology etc.

Being a versatile denominator in fraction may explain why we have 12 inches in a foot, 12 ounces in a troy pound, 12 old British pence in a shilling, 12 items in a dozen, 12 dozens in a gross etc.


Duodecimal fractions are usually either very simple

1/2 = 0.6
1/3 = 0.4
1/4 = 0.3
1/6 = 0.2
1/8 = 0.16
1/9 = 0.14

or complicated (X = 10)

1/5 = 0.24972497 recurring
1/7 = 0.186X35186X35 recurring
1/X = 0.124972497 recurring

Simple repeating fractions are rare because, 12 is between two prime numbers 11 and 13.

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