When it comes to using Platonic solids as dice, the d4 is something of a special case. There are precedents that stretch back into ancient history for the use of the d6, d8, d12 and d20 as dice, as all four of those solids, when rolled, will land with a single face up, visible to all parties watching. A tetrahedron, however, lands with a vertex up, one face down and three faces on display. As the example of the Zazz Polyspheres shows (their d4 is on the left above), simply putting a number on each of the four faces of a tetrahedron does not immediately turn it into what we know as a d4. For a tetrahedron to generate a random number between 1 and 4 that will be visible to people observing the die from all angles, some innovation was required.