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Underlying logic and design principles of different dice...

Posted: Sun Jan 06, 2019 7:17 am
by M Harold Page
Greetings all! I'm preping BFRPG for my daughter and her friends, meaning I'm returning to D&D-derived games for the first time in 25 years (have been doing Traveller & Fate in last few years).

I used to find the different subsystems with different dice illogical and irritating. Now I think I detect an underlying logic and this seems to be the place to ask: is it something like this?

Multiple Dice (e.g. 3D6): Avoided except for chargen and dramatic damage e.g from falling or big monsters. Lots of dice being added slows play, and makes it hard to manage multiple characters. Stats act as quasi hit points for Stat Bonuses, e.g. depleting endurance can deplete Hit Points.

D6: The default. Easiest dice to read and handle, particularly economical when there are lots of rolls to be made, e.g. party blundering through dungeon looking for traps.

D20: The second default, for when Stat and Level bonuses can effect the score, e.g. saving throws and combat.

Dx (e.g. D4): Used instead of modifiers. Raises or lowers the ceiling, but maintains a floor of 1.

D100: For when the focus is on the character because of having special abilities (e.g. Thief.)

Behind this seem to be the design principles:
  • For routine rolls, use a single dice, defaulting to D6 but using other dice in preference to +/- modifiers. This speeds up play, and enables the DM to handle multiple characters or repeated actions.
  • Where the focus shifts to a particular character, use % or multiple dice. This creates more numerical nuance, but also the increased physical/mechanical difficulty enforces that shift of focus.
Am I in the right ball park? If so, has somebody written a more informed blog post about this? (I've tried googling, and mostly come across sites trying to sell me packs of dice...)

Re: Underlying logic and design principles of different dice...

Posted: Sun Jan 06, 2019 8:52 am
by Clever_Munkey
Here are the some of Solo's words on the subject:

Here are mine:

To answer your question more completely:
Most of the reasoning behind the use of multiple dice is that the statistics make sense for the event within the game world. Multiple dice are used because it gives a wide range, and on a pseudo bell curve. This is good for things where very extreme values should be possible, but unlikely, but where there should still be some variance in the middle e.g. ability scores, large damage, hit-points, etc. Using 1dx (which includes 1d20, and 1d100) will give a flat distribution. This is good for answering "yes or no," questions. Do I break the door? Do I hit the goblin? Do I pick the lock? Different die sizes just result in different increments for probabilities. Every probability on 1d20, 1d10, 1d8, and 1d4 can be replicated on 1d100, but it's usually faster and easier to read the smaller ones, and obviously +1 to a roll is more or less important depending on the size of the dice.

Re: Underlying logic and design principles of different dice...

Posted: Sun Jan 06, 2019 10:48 am
by M Harold Page
Thanks! That's illuminating, especially the links.

Re: Underlying logic and design principles of different dice...

Posted: Fri Jan 11, 2019 9:46 am
by orobouros
It's all about the statistics. Tabletop RPGs were born from tactical board games from before computers were around, so you needed some way of generating random numbers. Historically, the "low" dice were associated with specific weapons: 1d4 for daggers, 1d6 for a short sword, 1d8 for a long sword, etc.

Dice choice also impacts how useful a bonus or penalty is. A +1 AC gives you a +5% chance to avoid getting hit. Nice, but not game changing on its own. A +1 to initiative (which is rolled on a d6) is a +16% bonus, pretty substantial. Rolling multiple dice gives you a regression to the mean, though it's not as drastic as you might think. (W40k orc players roll 60d6 and still get some pretty random results.)

Most systems that use d20 dice tend to default to d20 for rolls, though it can depend a lot on your DM since in old-school games the rules are more situational than fixed. At least with Basic Fantasy RPG, the rules are straightforward enough that just knowing them in your head isn't too hard after a few games. There's not really a default.