# Thread: RPG Game Mechanic Survey

1. Originally Posted by dulux-oz
True, but addition is commutative (a = b+c <=> a-c = b), so its the same thing - and easier to write AND understand (IMNSHO)
Edit 2: Okay, I think I need to make this make sense to myself more than anything. Your method is Die Roll (call it 12) plus Mod (call it +4) minus AC (call it 5) = 11 vs. TN. Great. But what is the Target Number? The order I gave, gives the value of TN. TN = THAC0 (1st level 20) - 5 = 15, or 12+4 = 16 vs TN 15. It isn't an issue of addition is commutative, rather it's a two unrelated equations being compared to see which is greater.

In other words, no, in this case it isn't commutative because it's (a+b = c ≥ f = d-e).

Original: Sure, but the point was that you're missing a step, since A + B - C = D ≥ TN, in this case, but you can't compare D to TN without first determining Y (THAC0) - D = TN.

Or, what I'm trying to say in game terms is d20 result + mod - AC = total ≥ TN = THACO - AC. Blah, maths classes were a long time ago for this. I think what I'm trying to say is that you can't get a result that needs to be equal to or greater than a Target Number that is determined by a different formula.

The way you put it sure, you'd know the result, but still not know the target number.

Edit: Must be getting late, I realize I'm starting to be redundant in different wordings.

2. Originally Posted by sjard
Edit 2: Okay, I think I need to make this make sense to myself more than anything. Your method is Die Roll (call it 12) plus Mod (call it +4) minus AC (call it 5) = 11 vs. TN. Great. But what is the Target Number? The order I gave, gives the value of TN. TN = THAC0 (1st level 20) - 5 = 15, or 12+4 = 16 vs TN 15. It isn't an issue of addition is commutative, rather it's a two unrelated equations being compared to see which is greater.

Original: Sure, but the point was that you're missing a step, since A + B - C = D ≥ TN, in this case, but you can't compare D to TN without first determining Y (THAC0) - D = TN.

Or, what I'm trying to say in game terms is d20 result + mod - AC = total ≥ TN = THACO - AC. Blah, maths classes were a long time ago for this. I think what I'm trying to say is that you can't get a result that needs to be equal to or greater than a Target Number that is determined by a different formula.

The way you put it sure, you'd know the result, but still not know the target number.

Edit: Must be getting late, I realize I'm starting to be redundant in different wordings.
OK, so I thought it was obvious (but maybe not): TN is the THAC0 (in both formulas, because both formulas are the same formula, just rearranged.

As you expressed it: (M is Modifiers)
1d20 + M >= THAC0-AC - which rearranged is
1d20 + M + AC >= THAC0 - which is how I expressed it - BUT yes, I did have the sign of the AC-term wrong - stupid me letting that typo past proof-reading (and that's what was almost certainly tripping you up)

And using your figures:
12+4 >= 20-5 == 16 >= 15 (a hit by a single point) - which rearranged is
12+4+5 >= 20 == 21 >= 20 (also a hit by a single point)

Does that make sense now (especially now that I've fixed up the sign of the AC-term)?

3. Yeah, the function change, plus the spelling out that THAC0 = TN helps. I kept sitting there going "Something isn't right here, but I can't quite put my finger on it."

4. Originally Posted by sjard
Yeah, the function change, plus the spelling out that THAC0 = TN helps. I kept sitting there going "Something isn't right here, but I can't quite put my finger on it."
It's all good - I'm just sorry I stuffed it up in the first place - nice catch!

5. RPG Game Mechanics
 Rolemaster Roll d100% and add Total Skill Bonus=Rank+Stat bonii. 101+ and you succeed. Later versions need 111+. Special and zany events occur on natural '66' and '00' results! Critical tables to add even more flavour to combat results, whether Spell or Arms!

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