This clock by Christiaan Postma consists of more than 150 separate clocks, each of them playing a role in a hybrid typographic/hand device to tell what time it is.
Christiaan explains the concept:
The word “three” completely appears when it’s exactly 3 o’clock and will then transform again as time passes. The word “four” begins to appear and at exactly 4 o’clock the word “four” is clearly visible. The word “three” is by then totally vanished and no longer readable.
Hard to visualize? Watch the accelerated animation below to see how it works.