This clock (supposedly made for kids) cracks me up. To tell what time it is, you have to do some simple math.
Here's its story:
The Albert Clock is named after Albert Einstein and inspired by an apocryphal anecdote: that Einstein was bad at math. Designer Alex Schindlbeck, who conceived this clock for a small Paris-based company, set out to turn classroom boredom into mental calculation skills. He gave the standard alphanumeric segment font a makeover, with improved readibility of numbers and mathematical symbols. This engaging educational tool caters to children's natural play instincts, and the satifsying delight of problem-solving.
The Albert Clock is only available at the MoMA Design Store (for $340!).