In this clock, the day of week and the hour are indicated using prime numbers.

There is the same number of primes up to 1000 and hours in a week. So it's possible to indicate what day and hour it is using a prime number in the range 2, 3, 5, ..., 991, 997.

For example, is the in the list. This is so today is the day of the week, . Within that day it's the hour, so the time now is .

For a different concept, try flipping the Symmetries switch.

In this clock, the time is shown using symmetries of geometric shapes (rotations that keep the shape exactly the same).

The seconds hand shows the symmetries of a dodecahedron. Each of the 12 faces can be brought to the front and rotated 5 different ways, for a total of 5×12=60 rotations.

The minutes hand shows the symmetries of an icosahedron. Each of the 20 faces can be brought to the front and rotated 3 different ways, for a total of 3×20=60 rotations.

The hours hand shows the symmetries of Klein's quartic curve. This surface cannot be embedded in 3-dimensional space, but is a quotient of the hyperbolic plane. If we tile the hyperbolic plane with heptagons, this quotient leaves 24 heptagons, and the 7×24=168 symmetries of their arrangement are the same as those of the Klein quartic curve. The view here shows this tiling using the Klein disk model.

For a different concept, try flipping the Symmetries switch.