A simple adding computer that uses marbles.

This is a very clever machine that can add numbers in a way that is similar to how a computer actually does it. Computers uses binary instead of decimal. In decimal (or 'base 10') you carry to the left when you exceed 10. For example, when you calculate 25 + 7, you have to carry the extra 1- that is, add it to the 2- to make 32. The 3 is the number of 10s and the 2 is the number of 1s. In binary (or 'Base 2') you carry to the left whenever you exceed 1 instead of doing it whenever you exceed 10. So 1 + 1 = 10 in binary: the 1 is the number of 2s and the 0 is the number of 1s. Can you figure out what 10 + 11 is in binary?

Computers only use binary because each 'bit' (storage unit) has only two states, that can correspond to either 1 or 0. This marble computer is the same: each 'bit' can either hold a marble or not, so it can either represent a 1 (marble) or a 0 (no marble). The cool part if the way it carries a 1 to the left- check out the video!