# Balance of Numbers on dice

Six-sided dice traditionally have opposite faces adding to 7, and this tradition is carried over (unquestioningly, it seems) to other dice. Is there a good reason for it? Why wouldn't you instead seek to make opposite ‘hemispheres’ as equal as possible, ideally arranging that the center of gravity of the pips is the geometric center of the die?

Added four years later: I recently did some searches: There are no ideal arrangements for D4 (obviously), D6, D10, D12; three arrangements for D8; 876 arrangements for the rhombic dodecahedron; and somewhere between seven and gazillions (the search is a long one!) for D20.

• To make the result more independent of how it's thrown. Can you make a D6 so fair that one can't learn to throw it with a preference for {6,5,4} over {1,2,3}? Feb 16, 2017 at 9:29
• MtG D20s actually have hemispheres, because they are used as health counters. Numbers are in order next to the face. So, 15 will be right next to 14 and 16, to make it easy to go up or down health. But without a reason to change the layout, why would game makers even bother? Feb 16, 2017 at 11:23
• @CyberClaw MTG spindown dice are also not legal for use in tournaments for the reason Anton is talking about; because a skilled player could learn to throw the dice so that it always lands in the higher range of numbers. A regular d20, on the other hand, is designed so that even if you could throw it so it would land in a general area, that general area would have both high and low numbers. Feb 16, 2017 at 15:33
• Surprised no-one championed this as off topic. Seems an appropriate question for history, engineering or math SOs to name a few. I guess games have dice so we get it here? Feb 17, 2017 at 15:49
• @joedragons, heh, well, I thought of taking it to Math but: isn't gaming the primary function of dice, and therefore the proper context for questions of their design? I wonder whether any other exchange has a ‘dice’ tag! Feb 17, 2017 at 20:18