Tuesday, October 11, 2011

d30 as Bell-curved d10

In working on the dice mechanics for the d30-based RPG, I'd created a set of tables showing how to roll a d30 as other types of dice (specifically d2, d3, d5, d6, d10, and d15.) This has more to do with the mechanic of the Action Table for resolving contests and challenges than it does with actually using the d30 to produce the types of results mentioned above (in parentheses.) But it did lead me to an interesting thought... what about using the d30 to produce a bell curve of results (like the ubiquitous 3d6 rolls we've all grown accustomed to.)

The 3d6 bell curve does have the advantage of making the extreme rolls (3 and 18) fairly rare (.46%) compared to how common the center rolls of 10 and 11 are (12.5% each.) While the extreme rolls on the d30 are about 7 times more likely to pop up than their 3d6 counterparts (with a result of 1 or 30 coming in at 3.33% chance each.) The 3d6 curve also allows for 16 different results, while the d30 curve only allows for 10. So let's take a look at how the d30 curve above compares to a 2d6 roll.

A 2d6 roll allows for 11 results (vs. the d30's 10.) But the general odds are much more in line with the d30, and they are: 2-2.78%; 3-5.56%; 4-8.33%; 5-11.11%; 6-13.89%; 7-16.67; 8-13.89%; 9-11.11%; 10-8.33%; 11-5.56; 12-2.78%. But with no "center" number like the 2d6 roll, the roller's highest chances aren't a single target number, but are split between the two center numbers.

So what it comes down to is this... the d30 as a bell-curved d10 is moderately comparable to a 2d6 roll, but is not substitution for a 3d6 bell curve.

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