The truth about THAC0

[weasel fierce]

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.

I'll use AD&D to refer to the pre-D20 editions (as they all works the same, hit roll wise) and 3.x to refer to the D20 editions.


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)


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)


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.



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.

 

[arwink]

Mechanically they're much the same.

In the mind of a new player, and many experience players, 3e's attack system is much more intuitive than THAC0. While I had players who couldn't tell me what AC they hit after a year of play in 2e, they picked up the 3e system in a matter of hours.

 

[Nathal]

They're weren't too many monsters in AD&D with ACs better than -7, right? A character with a THACo of zero would need to roll 7 or higher on a D20 to harm that creature. In 3E those numbers pale in comparison. The new rules seem to involve much bigger numbers than what earlier editions dealt with, but maybe I'm not remembering it right.

 

[Olgar Shiverstone]

The problem IMO wasn't so much THAC0 itself (though that was occasionally challenging as arwink describes), but that you had to have a table to look up THAC0 in the first place (let's see, I'm a fighter level 6, so I use this line, and ...). And a table for saves. And a table for monster attacks.

Now at least I don't need the tables.

 

[Angel Tarragon]

I picked up on the truth of the matter automatically when I first read the third edition PHB.

 

[Wild Gazebo]

It wasn't thac0 it was the inconsistency of the modifiers to AC and thac0.

 

[Crothian]

The problem IMO wasn't so much THAC0 itself (though that was occasionally challenging as arwink describes), but that you had to have a table to look up THAC0 in the first place (let's see, I'm a fighter level 6, so I use this line, and ...). And a table for saves. And a table for monster attacks.

Now at least I don't need the tables.

The THAC0 tables were just a forumal written out in table format. It was easy to memorize and figure out what the to hit number was. Saves most people wrote down and that was also easy. THe nice thing was the numbers wqere easy, no getting bonuses from a half dozen different sources like in d20.

 

[fanboy2000]

no getting bonuses from a half dozen different sources like in d20.

I wonder if that's why they went to the BAB system, they wanted a way to take diffrent bonuses into account.

 

[Viktyr Gehrig]

The THAC0 tables were just a forumal written out in table format. It was easy to memorize and figure out what the to hit number was.

Indeed.

2e:
Fighters reduce THAC0 by 1 per level.
Clerics reduce THAC0 by 3 per 4 levels.
Thieves reduce THAC0 by 1 per 2 levels.
Mages reduce THAC0 by 1 per 3 levels.

3e:
Fighters increase BAB by 1 per level.
Clerics and Rogues increase BAB by 3 per 4 levels.
Wizards increase BAB by 1 per 2 levels.

THAC0 was simple. It's saving throws that were a mess.

 

[Saeviomagy]

I'm pretty sure that thaco was not all that there was to it.

For instance: How many 19s and 20s were there on the end of the attack table? How many 2's at the other end?

I'm fairly certain that the table had something like 3 19s before 20... Can anyone tell me if I'm wrong?