There are 10 kinds of people in the world – those that understand binary and those that don’t.

 – This was on a wall poster in the NCIS “Doppleganger” episode from 2005.

Translation for those that “don’t”:  Binary numbers are just zeros and ones – on/off; up/down; in/out.  Think electric current and computers.

The first ten numbers in binary are: 1, 10, 11, 100, 101, 110, 111, 1000, 1001, and 1010.  So “10” in binary is “2” in decimal. 

If you see someone twitching their thumb in and out while raising and lowering the fingers on their hand, they probably are either counting in binary or have some sort of palsy.