Remember when you were a kid and you got those little spy kits that had the 3D writing thing where it supposedly hid the message, even though you could read it as long as you didn’t try and focus the two? Same concept, but with a clock.
The Seeing Double clock from ChillyChilly has the hours and the minutes transposed over each other in red and green. The hour and minute hands have different color filters on them, the hour hand is red, the minute hand is green, so when the minute hand is over one of the 12 locations, only the red shows through and its whatever minute marker that is, 5, 10, 15, 20, you get the idea.
In the same way, when the hour hand is over a spot only the green shows which is the hour, 1-12. Seems cool enough, costs $112.50 though, so its not cheap.
ChillyChilly Seeing Double Clock [via ohgizmo]