These fun and unusual dice were invented by physicist Heinrich Hemme from Aachen in Germany.
The result of the roll is not the number seen on the top face, but the arithmetic mean of the five visible faces. Black numbers are positive, red numbers negative. It may not be apparent at first glance, but just like a regular die, the opposite faces add up to 7!
Using the following procedure, the numbers 1 to 6 can be generated with equal probability:
- Roll the die.
- Add the visible black numbers.
- Subtract the visible red numbers.
- Divide the total by 5.
These dice are 22mm (7/8″) size – larger than usual to accommodate up to 16 pips on a side.