Forget your abacus? Lose your calculator? Every geek should know how to use binary to count to 31 on one hand. It won't replace your slide rule, but it is an attention-getter. If you're familiar with binary you'll pick it up quickly.
If you're new to binary, this isn't really a whole new counting system, you just have to think back to elementary school when you learned to count in base 10. And yes, I am aware of the cultural significance of numbers 4, 13, and 20. :oP
If you're interested in binary, you may want to check out my binary clocks.
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Geek Jokes
There are 10 types of people in this world. Those who know binary and those who don't.
Why did the programmer always confuse Christmas and Halloween?
Because Oct 31 equals Dec 25.
What do you get when you cross a lambda phage with a mountain climber?
Nothing. You can't cross a vector with a scaler (scalar).
What do you get when you cross and elephant and a grape?
Fun & Games
Count to 31 on One Hand