A dozen (common abbreviated doz or dz) is a grouping of twelve. The dozen may be one of the earliest primitive groupings, perhaps because there are approximately a dozen cycles of the moon or months in a cycle of the sun or year. Twelve is convenient because its multiples and divisors are convenient: 12 = 2 × 2 × 3, 3 × 4 = 2 × 6, 60 = 12 × 5, 360 = 12 × 30. The use of twelve as a base number, known as the duodecimal system (also as dozenal), probably originated in Mesopotamia (see also sexagesimal). This could come from counting on one fingers by touching the digits with one's thumb. ...