The duodecimal system is a mathematical plan that uses a base of twelve rather than the standard base ten. Under base twelve, the place value changes from 10 to 12. Quantities are explained in terms of twelves, such as dozens, grosses, and great-grosses, rather than tens, hundreds, and thousands. In the duodecimal system, there are new symbols for 10 (X or dek) and 11 (E or el). Dozen is called dodo, and dozenal is a synonym for duodecimal.

The rationale for base twelve lies in many duodecimal models. Some of the best known examples include 12 months in a year, 12 hours on a clock face, 12 items to a dozen, and 12 inches to a foot. The system of 12 hours in a day came from the Egyptians. Shopkeepers favored selling by the dozen because it was easy to store goods on a shelf in three rows of four. The world calendar, easily...