Let's Talk About THAC0

[Bacon Bits]

I have not read the rest of the thread; however, I have opinions.

I feel like THAC0 gets a bad rap. It's the precursor to 3E's Base Attack Bonus, and came after 1E's attack matrices. It's actually super simple.

The important thing to remember is that it's the exact same math, but in reverse.

In 3E-5E, you roll d20 and add a bonus in order to beat the target's AC.

In 1E-2E, you roll d20 in order to beat THAC0 minus AC.​

So instead of adding a number to your d20, you simply deduct a number from your THAC0. Same maths, just minus instead of plus.

If your THAC0 is 15, and your target's AC is 2, you need to roll 13. It's that simple! (Remember, lower AC was better).

I feel sorry for poor old THAC0. It has a bad reputation for being complex, when it's exactly as complex as the current method!

No, it's not just as complex as the current method. It's only the same complexity when you already know the target's AC. Since AC varies between targets and is typically a secret number until the players manage to work it out, THAC0 is not less complex. Players can't do die roll + AC >= THAC0. Players have to do Die roll - THAC0 = AC hit. Except that's wrong. They actually have to do THAC0 - Die roll = AC hit. Did you notice the error while reading, or did you have to stop to think about it? Is it obvious which is correct? If your THAC0 is 15 and your modified roll is 13, is it easy to intuit while rolling the dice that you hit AC 2 and not AC -2? Not really. It's hard to look at the dice and say, "Okay, that's not possible you must've done the maths wrong because that result is way off." You can't do that because 90% of the time your results are between -5 and 5. All your numbers look the same. And now you add in a modifer, and it gets really complicated. See, it's really easy to confuse THAC0 - Die roll - 1 = AC hit and THAC0 - (Die roll - 1) = AC hit. The room for math errors in how people actually use THAC0 is significant.

The real problem with THAC0 is that the "easy" mode formula of die roll + AC >= THAC0 conflicts with player nature. When players roll an attack die, every player -- and I do mean every player -- wants to know "What AC did I hit?" That's the question they always pose. It's one of the most common questions asked at the AD&D table. Players can't measure in their performance *against the other PCs and NPCs* without doing that step. In order to understand how well their character is doing -- how powerful they are -- knowing the target number they reached is vital. THAC0, in it's "easy" mode, seeks to obscure that information from the player by design. Gygax assumed the player would never know their THAC0. That's why the charts were in the DMG. Gygax assumed only the DM would determine the outcome of an attack because the DM would be in total control of everything. In reality, that's too much burden on the DM to look up tables all the time. So everybody made the players do it. Except the players want to know how well they're doing. Unless they roll high or low, they won't know. And then they'll only know they rolled high or low.

The lesson of THAC0 and descending armor class is clear: You cannot design an action resolution system around how you want people to play. You need to design them around what makes game play operate swiftly, intuitively for the players and the DM, it must be easy to evaluate by the players and DM so they can understand the consequences of modifiers, and it must help all players and DMs at the table understand what's going on and maintain the suspension of disbelief. It must be fast to resolve, it must not be prone to simple math errors, and it must not occupy more game time than it absolutely must. THAC0 and descending armor class essentially do none of that.

 

[Charlaquin]

There's more historical revisionism going on here than a typical grade school U.S. History class.

THAC0 was awful. Negative AC was awful and un-intuitive. We only put up with it because we didn't know any better.

Now we do.

Maybe for your group. For as long as I’ve been discussing games on the internet there have been people who claimed to have genuinely preferred THAC0. Personally, I didn’t start playing until 3.5, my analysis is based purely on my understanding of game design and psychology.

 

[Charlaquin]

Why would you know your target number before you roll with THAC0? Is the DM telling you your opponent's AC?

No, it's not just as complex as the current method. It's only the same complexity when you already know the target's AC. Since AC varies between targets and is typically a secret number until the players manage to work it out, THAC0 is not less complex.

You know, I think I may have discovered the key factor in whether or not someone liked THAC0.

 

[Slit518]

I feel like THAC0 gets a bad rap. It's the precursor to 3E's Base Attack Bonus, and came after 1E's attack matrices. It's actually super simple.

The important thing to remember is that it's the exact same math, but in reverse.

In 3E-5E, you roll d20 and add a bonus in order to beat the target's AC.

In 1E-2E, you roll d20 in order to beat THAC0 minus AC.​

So instead of adding a number to your d20, you simply deduct a number from your THAC0. Same maths, just minus instead of plus.

If your THAC0 is 15, and your target's AC is 2, you need to roll 13. It's that simple! (Remember, lower AC was better).

I feel sorry for poor old THAC0. It has a bad reputation for being complex, when it's exactly as complex as the current method!

I started with 2nd edition in 1999 when I was in high school.

Never had a problem with it, and enjoyed it.

Getting Armor Class to the negatives was a fun challenge.

I too miss Thac0.

For those of you who don't know, in case it wasn't mentioned - Thac0 stands for, "To Hit Armor Class 0."
So, if my character's Armor Class was 0, your Thac0 would tell you what number on the d20 you would need to roll (or higher) in order to hit me.

Thac0 - pronounced: th.aaa.co

 

[Voadam]

THAC0, in it's "easy" mode, seeks to obscure that information from the player by design. Gygax assumed the player would never know their THAC0. That's why the charts were in the DMG. Gygax assumed only the DM would determine the outcome of an attack because the DM would be in total control of everything.

I think this is a good point. I remember trying to do that as a DM, to have the player roll and know that rolling high is better and that they have some bonuses and that some classes are better than others, but I as the DM would handle the specifics and they could focus on the experience and not worry about the mechanical numbers. In essence I would be most of the computer handling the mechanics behind the scenes and they could have more of a narrative experience.

But that is a big pain to handle as a DM.

Also many people are both players and DMs so they can legitimately see the stuff in the DMG so the pure player experience is an obvious myth, many players know the mechanics.

Then there were 1e character sheets with THACO done out for the PCs to see on their sheet and many people played with saying "I rolled an 11, I hit an AC of 3" which helps the DM adjudicate combat faster and can make play smoother.

Then 2e felt great with putting THACO and saves in the PH so they were expected part of PC knowledge and the DM would be less speed bumped whenever they came up.

 

[Sacrosanct]

The real problem with THAC0 is that the "easy" mode formula of die roll + AC >= THAC0 conflicts with player nature. When players roll an attack die, every player -- and I do mean every player -- wants to know "What AC did I hit?" That's the question they always pose. It's one of the most common questions asked at the AD&D table. Players can't measure in their performance *against the other PCs and NPCs* without doing that step.

This sounds like it might be a shock to you, but no, lots of players couldn't care less how much their PC did in power compared to the other players. Most people I gamed with since the early 80s had the idea that the game was a team sport, and who cares if Bob did 1 or 2 more damage per round as long as I had fun with my PC.

And no one asked, "What AC did I hit" because you knew what AC you hit as soon as you rolled. That's what THAC0 is, literally. You roll your attack dice, and subtract the result from what your THAC0 is. That simple. If my THAC0 was 18, and I rolled a 14, I knew I hit AC4 or worse. THAT'S what players called out in combat. Not "What AC did I hit?", but "I hit AC4" and the DM would reply "that hits" or "that's a miss."

THAC0, in it's "easy" mode, seeks to obscure that information from the player by design. Gygax assumed the player would never know their THAC0. .

Wait, what? Of course players knew their THAC0. It was right there on their character sheets. Like, literally right there! If players weren't meant to know their THAC0, the design team did a pretty bad job at it.

 

[Sacrosanct]

In case you're curious, these are the character sheets from pretty much the beginning: Moldvay's basic, and 1e (note how players knew what they needed to hit because there were sections for it on the sheets):

 

[Charlaquin]

Wait, what? Of course players knew their THAC0. It was right there on their character sheets. Like, literally right there! If players weren't meant to know their THAC0, the design team did a pretty bad job at it.

I’ve observed that many players, especially players who started with 3e or later, conflate THAC0 with descending AC generally. I know it took me an embarrassingly long time to realize that THAC0 was not shorthand for descending AC, but in fact referred to a 2e evolution from AD&D’s Attack tables.

 

[Hussar]

Did you do it differently? I guess I never considered the possibility that the DM might just ask you to roll and tell him the number you got and your THAC0, do the math himself, and tell you if you hit or not. That sounds awful, it’s no wonder it developed such a bad reputation if folks were doing it that way.

I'd say yeah, that's typically the way it was done. Prior to Thaco, you'd have a matrix on the DM's screen, so, again, you call out your attack number, and the DM consults the matrix to tell you if you hit or not. AFAIK, that's typically the way it was done, so, virtually all the math was dumped on the DM to figure out.

Of course, after saying that, I realized that my group would generally just tell me what AC they hit. "17, that hit's an AC 3, did I hit?" was a pretty common phrase.

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edit to add

BTW, was it really that hard to get into negative AC's in 2e? Full plate and shield was AC 0 and that was generally affordable by about 3rd or 4th level. Add in any magical protection (+1 shield, ring of protection) or even a 14 Dex and you have a negative AC. Drilling your AC down to near -10 was certainly do able in the games we played. By about 7th-10th level generally.

 

[Thac0 the Barbarian]

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