This beautiful clock takes advantage of the fact that if you place a diagonal line on a rotating base, it'll trace out a hyperbola shape in 3D. The hours are marked on the clock, and whichever one the hand is pointing to will show you the nearest hour.
An attractive adornment for any desk or horizontal plane, this is also a demonstration of the concept of a ruled surface. Oh, and it tells the time.
The clock measures 12cm in height and has a base diameter of approximately 11.5cm.
Price = p550 pence = £39.89