weasel fierce said:
THAC0 is always raised as the big thing that made oD&D and AD&D totally unplayable. (for D20, the counterpart tends to be attacks of opportunity )
So lets deconstruct the math and see how it works.
The math itself is not necessarily what makes something totally unplayable. There's no maths involved in Attacks of Opportunity.
weasel fierce said:
Finding out what you need to roll equal to, or better:
3.x: Deduct Base attack bonus from armour class. Result is number you roll equal to or better to hit.
AD&D: Deduct armour class from THAC0. Result is number you roll equal to or better to hit.
(Exactly the same)
Finding out what armour class you hit with the number you just rolled:
3.x: Add the rolled, modified number to your base attack bonus
AD&D: Deduct the rolled, modified number, from your THAC0.
(the same, except one is a deduction instead of a plus)
Although any mathematician would tell you an addition and a substraction are the same thing, it is true for computers and calculators, but less so for a human brain. It's always better to have to add than to substract.
weasel fierce said:
Basic to hit roll mechanism:
3.x: Roll 1D20. Add base attack bonus. Equal or better than armour class is a hit.
AD&D: Roll 1D20. Add targets armour class. Equal or better than THAC0 is a hit
(exactly the same)
No it isn't. Mathematically, saying that an addition followed by a comparison is the same thing as another addition followed by another comparison. But mathematics are not the only thing involved. I'll address this point below.
weasel fierce said:
Looking up numbers on a chart ? Both versions use two single numbers to determine attack success, both of which would be written on your character sheet, and unchanging till next level (Thac0 / BAB and armour class)
Then there's armour class.
3.x AC: Number shows how hard it is to hit you. Thus, a high number is good.
AD&D AC: Number shows how easy it is to hit you. Thus, a low number is good.
THIS is the point. In d20, you roll your attack "skill" (BAB), and you have to beat your opponent's skill at evading attacks (AC). Simple, straightforward, intuitive, logical.
In AD&D and previous, you roll your opponent's skill at being hit (AC) and you have to beat your own propensity at failing miserably in your attacks (THAC0). This is totally counter-intuitive.
weasel fierce said:
Saving throws are the other thing, but I'll leave that for another day.
Mind, this isnt an edition war attempt but a basic deconstruction showing that THAC0 works almost exactly identical to the D20 system.
THAC0 is a Bizarro world's BAB. There are similarities, but the logic behind THAC0 probably only makes sense for Fungi of Yoggoth. The d20 combat system is active (you act and must overcome challenges, i.e., you roll your own skill and must beat a target number), the AD&D combat system is passive (you roll for your opponent, but not for you) and pessimist (you don't hit because your skill is better than the opponent's, but because you're less clumsy than him).
