On Rolling Dice

I’m implementing skill checks in BFD right now and got to wondering about dice probabilities. One of the things I wanted to try and avoid is using pure probability values in the belief that by using a dice based system people will have an easier time visualising what’s going on behind the scenes and can discuss it better. I also want to attract fans of tabletop gaming.

I have experience mostly with DnD and Games Workshops games and to be honest I always felt that both of them are lacking in opposite areas.

DnD (4e specifically) is as you hopefully know a D20 based game where your normal skill check is to roll a D20, add your modifiers to it and see if you beat the  target skill. This results in some very large numbers being thrown around which can get a little confusing and having double the skill not always meaning you’re twice as likely to succeed.

GW games on the other hand prefer stats that only tend to range between 0 and 10 with 3’s being considered “average”. Most skill checks with their systems depend on looking up the two stats involved and finding a target value for a D6 roll. Normally if the two stats are equal then this would be a 4+ (50%) if your is 1 more than your opponents it’s a 3+ (66%) and if it’s more than double it’s a 2+ (83%).

I like the small stats of GW games but not the probability distribution. If I have double the weapon skill of my opponent I should be twice as likely to hit them (75%)  and if I have triple their skill I should be twice as likely again (88%).

These values only come up when dealing with re-rolls though. A 4+ on one D6 with a Re-roll is a 75% chance of success (and with 2 re-rolls it’s 88%). So I could say that having double the skill of the target lets you reroll a failure and triple lets you reroll two failures. This sounds great but it makes having a slight 1 or 2 point advantage useless.

So I ask the tabletop playing public who have no doubt done the maths on this already: Is there a dice system that would give me the distribution I crave with the granularity needed?

4 thoughts on “On Rolling Dice

  1. I can’t really answer your question – but YEARS ago I was one of a group of people who created an RPG in Javascript (this is when Javascript was the latest thing!!)

    One of the more interesting things I learned was that people didn’t trust ‘computer dice’. They hated that they just typed a command/pressed a button and a number appeared. They claimed that it ‘took the skill out of it’.

    Now I’ve no idea how much ‘skill’ people can have in throwing dice but I definately know people THINK they have skill – e.g. that they can influence which side a die lands on.

    Whether you’d be interested in considering that aspect of it – or even if it’s possible to do – I’ve no idea, but I thought I’d throw it in 🙂

    • It absolutely is possible to influence real dice by how you roll them (It’s called a practised roll) and if I catch my opponent doing it in a tabletop game then they are going to get a smack because it is cheating in my opinion. Essentially by making sure the dice only rotates around one axis and does a full rotation you can vastly increase the chances of it landing the same way up as you were holding it. This is why at a craps table the dice have to hit the far wall.

      I already have a completely fair RNG for the game hooked up that uses a scrabble bag method of number picking which gives the appearance of being fairer than a truly random number generator when smaller numbers of dice rolls are involved.

      I’m hoping people will realise that the skill to the games is not in rolling dice but in picking which abilities to use, positioning and how the party of characters interact. I find that RPGs that completely remove random chance end up feeling a bit soul-less. Blood Bowl wouldn’t be anywhere near as entertaining if it wasn’t for the possibility for the dice to go against you.

  2. Why don’t you use physics to let the dice fall, then God can decide the outcome? oh wait, God doesn’t play dice. Well, instead let NVidia decide.

    A practiced roll is a kind of trained effort coming from the player (a skill); while you don’t need to actively reward it, it is reasonable to allow it because then you’re letting the player do what they want to do, and they’re competing against the dice, which is really the point of dice.

  3. Honestly, anything involving just two dice works well.

    Even just converting a d20 style system over to 2d10 instead of 1d20 gives you just enough centralization to make things feel comfortable without having things be overly uniform (once you’re rolling more than about 3 dice.. each roll feels samey) unless you’re using a dice pool system.

    One thing a lot of systems (including my own homebrew RPG) use is a pairs of dice that step up with skill

    you’d have something stats like

    MUSCLE: 1d6
    BRAINS: 1d8
    QUICKNESS: 1d6

    and skill something like

    FIGHTANS(MUSCLE): 1d8
    SHOT GUN(QUICKNESS): 1d6
    LEARNIN'(BRAINS): 1d4
    WHEELIES(QUICKNESS): 1d6
    TALK MAN(BRAINS): 1d10
    DANCIN’ (QUICKNESS): 1d12

    They’ll tend towards their averages more than on a single roll system, but not so much that high/low rolls are a lost cause. You check against static numbers (ala D&D) but tend not to have much in the way of +s or -s. Even a +1 or +2 as static roll modifier is very powerful, so you don’t get the laundry list modifiers.

    I’ll say that while I like these kind of systems the best, dice pool systems also work well.

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