dice
I've just bought a d8, and noticed that the number arrangement is different from my other one. My new die has only even numbers on one half, and only odd on the other half. My old die has 1,8,5,4 on one half and 2,3,6,7 on the other.
Is there any correct pattern for it?
Does it make any difference?
There sure is!
With a pool of 4d20 I get the following results in Excel (using a total sampling of 10,000 rolls):
1 2 3 4 5 6 7 8 9 10
9% 8% 7% 6% 5% 4% 3% 3% 3% 2%
11 12 13 14 15 16 17 18 19 20
2% 3% 3% 3% 4% 5% 6% 6% 8% 9%
So roughly a 20% chance of critical success or critical fail, and a 4% combined chance of a 10 or 11.
Credit goes to sage for suggesting the even/odd roll instead of a coin.
And now some graphs, because everyone likes graphs, right?
Although technically this is bar-graph land, I included a line graph as well as I thought it made it easier to see in light of the number of bars that were being dealt with. I also increased the sampling to some 100,000 dice.
You're not missing anything. Based on the description you provided, it sounds like your player purchased one of Q-Workshop's licensed "Call of Cthulhu" dice sets. Strange as it may seem, the license isn't to the roleplaying game necessarily, but to the story by H.P. Lovecraft and the associated Mythos iconography. The set of dice is decorated to look appropriate for Cthulhu-themed games, but isn't designed for a BRP Call of Cthulhu game — they're the seven dice usually found in D&D and other popular roleplaying games.
Best Answer
There's no correct pattern, and in a fair die it makes no difference.
In practice, most standard dice sets are not entirely fair, because of how they're tumble-polished after removal from the molds.† How an unfair die is numbered can make it more unfair if the manufacturer decided to cluster all high (or all low) numbers near each other. Few manufacturers do this though, exactly for that reason—both your dice mix high a low numbers in each half, just in different ways.
However, the imperfect shape caused by tumbling affects the "rounder" dice more (such as the d20), and it's unlikely for a d8 to suffer noticeable unfairness.
† Due to demand for fairer dice, manufacturers such as GameScience and Chessex make dice that haven't been tumble-polished.