Digits & Place Value

Why is 9 the biggest single digit? Not because of nature — because of a choice. We count in base 10, so a digit runs from 0 to 9, and the moment we reach ten we 'carry' into a new column: 9 + 1 = 10, meaning 1 ten and 0 ones. Change the base and the largest digit changes with it. In base 2, the largest digit is 1 — and 1 + 1 = 10.