Percentile Checks

Last time I talked about task resolution I discussed OD&D's X in 6 chance system. I like that system a lot, but there are also other ways of resolving activities in the game. If you want a more "AD&D' style system, switch to percentile checks. I've noticed almost everything in AD&D (at least 1E for the most part) has the percent chance listed next to it. Even if it is checked using X in 6 chances on a d6, or X in 10 chances on a d10, there is usually a percent listed in parenthesis. Several sub systems, as well, take advantage of the percentile dice: grappling, and disease spring to my mind as some examples.

This is an extremely simple, easy to grasp, and easy to convert to system. If you're using the AD&D books, use the percent chances listed. If it's a X in Y chance roll (found in OD&D, B/X, and AD&D), simply find the percent chance using basic math (X divided by Y). With the d20 system this becomes slightly more problematic. You can use the DC+1 (difficulty class), divided by 20 to come up with the percentage chance for an unmodified roll. For every plus +1 it increases +5% chance, and for every -1, it decreases -5%. If there is a usual modifier, (like an attribute check), you can subtract the modifier from the DC, add 1, and then divide by 20. The reason it's problematic is that the point of the d20 system, is to constantly be changing modifiers. But it can work. If you're using this system, it's doubtful you'll be using much d20 system material anyway (or you'd just stick with the d20 system). (Note that +1, accounts for the fact the roll is EQUAL or better than, not just better than.)

Some of the most obvious benefits of this system is that it's pretty common sense. If you're Referee is good with math, has some life experience, then coming up with chances for actions can be pretty easy. It's also straight forward: when you say you have 50% chance, people know what it means, so it makes it even easier on players to decide what to do, or to negotiate wit the Referee on what's fair. If you take the time note the most common tasks in your games, you won't need to make it up on the spot much anyway. In fact this is what I plan to do; go through all the fantasy games I have, and note down percent conversions for tasks that are common in my games, or may come up. In fact, this opens you up to converting material from so many games (Runequest, BRP, Arduin, Chivalry & Sorcery, etc.).

As far as "modifiers", there are at least two routes you can go of, that I know of. I might make a universal table, like the Thief modifiers, that gives simple percentage modifiers based on attributes, for relevant tasks. No more than a -15%/+15%. In this fashion, you have the most simple (and closer to the d20 system), plus and minus modifiers. If you want it to hew a little closer to most d100 games, you can use multipliers, and division.

For attribute checks, you can use the method mentioned above, or you can use something closer to BRP's, attribute x 5. If that's too easy (it can yield up 90% chances), you can use x4 (12-72%), or x3(9-54%) even. In Call of Cthulhu, the multiplier can even be based on the situation's difficulty. I'm not sure which one I'll stick with, but I'm leaning more towards the above, since it's simple.


Of course there's always the old school option, and use percentage and other options. Use 3d6 roll under for attribute checks, X in Y chances for racial abilities, d% for adventuring tasks, etc...

As a final word, I'll just restate what I've said above. I like this system a lot, because I'm going to be able to come up with a list of common adventuring tasks, and determine their percentage chances, with some common modifiers. It's simple, easy to grasp, and really straight forward. Furthermore, this list will be for the Referee only, so I will request rolls when I think their needed. It won't be a player tool to turn the game into "roll-playing".