The Percentile Dice Problem
Authored by Mr. Z. ~2 min 38 sec
Foreword
Percentage-based odds have been a staple in tabletop roleplaying games since TSR's brown books and were present in wargames long before that. This is to say that since the dawn of ten-sided dice, men have argued about how to roll percentages. In this brief rant I'd like to offer my two cents and ultimately two relatively simple solutions to this issue.
The Problem
Many TTRPG systems use illogical rules to generate a result from 1-100 on a set of two ten-sided dice (d10s). For example, below is an excerpt from the "Using the Dice" section of Basic Fantasy 4th Edition:
A pair of d10's are also used together to generate numbers from 1 to 100, where a roll of 00 is counted as 100. The two dice should be different colors, and the player must declare which is the tens die and which is the ones die before rolling them! (Or, the player may have a die marked with double digits, as shown.) Rolling two d10's in this way is called a percentile roll, or d%.
This rule looks agreeable after a cursory glance. My issue lies in the aside noting that a double-digit d10 is identical in use to its single-digit counterpart. This same rule is more explicitly present in the basic rules for Dungeons & Dragons 5th Edition:
Some ten-sided dice are numbered in tens (00, 10, 20, and so on), making it easier to distinguish the tens digit from the ones digit. In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.
Ultimately, this does not make a whole lot of sense - on a roll of 0 and 00, the game claims that the result is a 100. What does a roll of "0" and "90" yield? These rules would suggest 90. I am here to tell you that the sane result is 100.
Solution One: Logical Interpretation
Why does the "0" on a single-digit d10 suddenly become a "0" instead of a "10" when one rolls percentile dice? The answer seems to be: FOR NO GOOD REASON!
My simple solution is one of absolutes. "0" on a single-digit d10 is always read as 10. Thus, a "00" on a double-digit d10 thus now always read as 0. A few examples of dice read in this manner are found below:
90 + 0 = 100
00 + 0 = 10
00 + 1 = 1
50 + 7 = 57
30 + 0 = 40
30 + 9 = 39
This eliminates essentially all confusion when a percentile roll is interpreted - it's so simple that I almost feel like no further explanation is required. Gone are the days of newbies wondering why a 10 suddenly changes to a 0. Gone are the various interpretations of 00 + 0 and the horrifying implication that a result of 0 could somehow be rolled.
Now while this solution is elegant, I admit it has its problems. New players may wonder why a roll of 0 + 0 on two single-digit d10s is 100, but a roll of 00 + 0 is 10. To this I say if your players are new the GM should probably "lay down the law" and mandate a certain method of d% rolling and interpretation.
Solution Two: Death to the Double-Digit Die
One may argue that this problem is entirely manufactured. I agree! That's a large part of what pisses me off about it. The problem would be solved if dice sets came with two single-digit d10s instead of a single-digit d10 and a double-digit d10. This is not to mention that the double-digit d10 is incredibly useless to have in one's kit - new and veteran players alike instinctively reach for a single-digit d10 to roll a result from 1-10.
This perfectly solves my problem with percentile d10s, and results in an RPG dice kit that is ultimately more useful than what we currently shell out our hard-earned dollars for! Further, no modifications to rules in books need to be made aside from the omission of double-digit d10s entirely.
This is the true solution in my opinion. Turns out the grognards had it right once again.
Takeaway
To make the results of percentile dice more intuitive for new players, make it so the single-digit d10 has absolute results, instead reading the more unusual "00" as 0 and using basic addition (00 + 0 = 10, 90 + 0 = 100.) Or, even more simply: give the players two single-digit d10s with a set!
This rant has ended. Thanks for reading!