" But when you want to mark a number on an abacus, what do you do if there are no stones in a column? The number 60 is one wedge in the sixties column and no wedges in the ones column. How do you write “no wedges”? The Babylonians needed a placeholder that represented nothing. They had to, in effect, invent zero. And so they created a new character, with no value, to signify an empty column. They denoted it with two slanted wedges. "
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