Even if the mention of trigonometry, calculus, or algebra gets your heart racing and your palms sweating, you still might appreciate this watch that demonstrates the first proposition in book one of Euclid's Elements. Because even if you don't know what that means, you can still look like you do, while still easily telling the time.
The first proposition pertains to using two circles to draw an equilateral triangle (all sides are the same length) when you're given a single horizontal straight line to start. As this video demonstrates, it sounds much more complicated than it really is.
So what makes this $36 watch fun is that the two circles and equilateral triangle used as its spinning hour, minute, and second hands actually perfectly line up twice a day to show proof of Euclid's Proposition 1. It's certainly a little nerdy if you're in the know, but it can also just pass as a piece of modern abstract art on your wrist. Unlike a calculator watch, which leaves no doubt as to your true leanings. [ThinkGeek]