Granularity in Checks

Let me briefly praise OD&D for the granularity level in its different checks. Perhaps even a theory of granularity can be initiated from this:

The closer the PC's are to combat and mortal peril, the higher the granularity used -- and hence the higher the detail in the rules for that system. For attacks and saving throws, we use d20's, that is, 5% increments; we can fairly finely tune and "game" the numbers in play when the PCs are in a life-or-death situation.

But as we get further away from that situation, the granularity is reduced. We use d6's (17% increments) for things like searching, listening, finding secret passages, and opening stuck doors. When we're in "exploration" mode, death is not so obviously at our throats, the peril not as great, and therefore there's no need for the same level of detail in the mechanics, nor space given for a multitude of bonuses and modifiers (or even time for the die in question to roll to a stop on the table).

Now, we can admit that this was possibly a historical accident. Chainmail introduced a game system with everything based on d6's. Original D&D presented the option to use d20's in combat as the optional "Alternative Combat System". EGG later went completely off the farm with Greyhawk's percentile-based Thief skills for hiding/ sneaking/ pickpocketing/ trap removal (although in 5% increments, so they could have just as easily been d20-based) -- and again in places like Oriental Adventures, which introduced d20 skill checks for generic things like riding, poetry, and tea ceremonies.

This latter tradition was, of course, carried forth to the 3E d20 System. But we can see why the desire for a "unified mechanic" (every check on a d20, say) may be fundamentally flawed in this specific sense. When every check has the same granularity, then there is the implication that every check is equally meaningful, and deserves an equally detailed treatment in the rules system. It poses as an invitation to develop equally numerous modifiers, bonuses, and benefits to every different kind of check. And perhaps we should prefer to inhibit that in certain areas.

Keeping the high-granularity checks (d20's) reserved only for combat situations and/or mortal peril actually serves as a fairly good existential simulation of the adrenalized, time-slows-to-a-crawl, see-everything-in-detail nature of the life-or-death experience. It may have been an accident that OD&D exhibited that methodology, but perhaps it's one that deserves emulation.


  1. I'd never considered this facet of OD&D. Your post does make an excellent point, though. As you said, whether this was an accident of history or a design notion is not certain.

    Another example of how the Greyhawk Thief's skill system still feels wrong in OD&D.

  2. What an amazing insight! It certainly rings true to me.

    I'm going to bring this up to my 4E group of friends and see what they might have to say.

  3. Very interesting. My math skills are limited (at best), but I'm certainly interested in it - in how it is applied to gaming too.

    I keep coming back and re-reading this subject, feeling like there's an epiphany lurking somewhere nearby...


  4. Late comer i am, but Im new to 0dnd and am tooling around with a basic skill system idea of everything is at a 2 in 6 chance base modified by attributes
    If a skill roll would be a 0 in 6, you'd have to roll a 1 then a 3 or less on a second die, and if the skill roll would be a -1 in six you'd have to roll two ones in a row to succeed.

    loving the blog. this and a couple others are my new addiction.

    1. Interesting, thanks for the comment!

      (You might consider the bonus for 3 or 18 just being +/-2 like I do, already a pretty massive swing on a d6... and then you can drop the -1 target case, and also extend smoothly for 19-21: +3, 22-24: +4 etc.)