This is already concisely explained in the article The Mesopotamians’ unique counting method is thought to come from a mix of a duodecimal system that used the

This is already concisely explained in the article The Mesopotamians’ unique counting method is thought to come from a mix of a duodecimal system that used the twelve finger joints of one hand and a quinary system that used the five fingers of the other. By pointing at one of the left hand’s twelve joints with one of the right hand’s five digits, or, perhaps, by counting to twelve with the thumb of one hand and recording multiples of twelve with the digits of the other, it is possible to represent any number from 1 to 60. How is the long winded Wikipedia article a better explanation?