Coin flip

A coin flip gives heads or tails with equal probability. This one draws from the browser’s cryptographic random number generator rather than a simple pseudo-random function, so the two outcomes really are equally likely. Flip once, or flip several hundred at a time and watch the tally converge on fifty–fifty.

A real coin is not quite fair. Persi Diaconis and colleagues showed in 2007 that a flipped coin lands the same way up as it started about 51% of the time, because it precesses rather than rotating cleanly. A digital flip has no such bias, which makes it the fairer of the two even though it feels less trustworthy.