Thac0

[FreddyNoNose]

On another website, someone is saying that THAC0 is complicated. Does anyone else feel it is complicated? It seems very simple to me.

[MeeposFire]

Well for some it is since subtraction is not as simple on a whole as addition. Granted some people make way too much of a deal about it but it is slightly less intuitive than addition.

It also depends on how you do it. I have no problem doing it how the 2e PHB describes how to do it but I have seen other people explain how to do it a different way that makes sense to them and I cannot use it at all.

[Potatomade]

My group is relatively new to 2E, and for some of us, it was extremely hard to figure out, to the point where people preferred playing casters just to avoid it. Now though, except for the guy who has to count on his fingers, it's just as fast and natural to us as d20.

[Nerd-o-rama]

It's not so much complicated as it is counterintuitive. Rather than just adding modifiers to a die roll and comparing it to a static value, you're changing the static value (AC) and then adding it as a modifier to the attack roll, then comparing it to a number on a chart which is the real target value. Also, the books tend to explain this in different ways that work out to the same result, at least if my fuzzy memory is correct.

It's still the same mechanic as d20, it's just explained in a convoluted way.

[Dimers]

THAC0 and AC both have low numbers stronger. One downside to that, regardless of whether it's simple to use, is that some writers/creators don't express things right. They'll say "+2 AC" for an obviously defensive benefit, that kind of thing. The core books don't have that problem but it crops up in a lot of other places.

[Anonymouswizard]

Yeah, some people just hate subtraction for some reason. Although it takes longer for some people, they generally aren't great at mental maths.

If you know you have the weapon, you can actually just subtract your attack bonuses from your THAC0 (or add your penalties). That way the formula goes from THAC0-(1d20+modifiers)=AC hit to (THAC0-modifiers)-1d20=AC hit, but we already know (THAC0-modifiers). It's equivalent to adding your modifiers to your BAB.

Basically, people overstate it and some seem to loathe addition. What's bad about THAC0 isn't that it's difficult, it's that it contributes to the 'are high or low numbers good' problem.

[Potatomade]

What's bad about THAC0 isn't that it's difficult, it's that it contributes to the 'are high or low numbers good' problem.

Which I think of as a perk, honestly. By having combat require high d20 rolls and ability/NWP checks require low rolls, you mitigate the problem of having a wonky die. Once, a guy in my group rolled ~30 1's over a given night. It was ridiculous, like every other roll was a 1. It kept happening even with other people rolling the stupid die. But, because it was for both combat and NWP checks, he wound up being useless in combat, but great in every other way. Which at least made things more interesting than if he suddenly started failing everything.

He doesn't get to roll that die anymore, though.

[Altair_the_Vexed]

THAC0 isn't really very confusing or utterly bad, but once you've done it the other way (AC = target dice roll), then you have to wonder what the hell they were thinking.

[Kish]

Lots of people have trouble with THAC0. I remember that already being the case back when 2e was the most recent edition and there was nothing simpler it was being compared to.

[Anonymouswizard]

Which I think of as a perk, honestly. By having combat require high d20 rolls and ability/NWP checks require low rolls, you mitigate the problem of having a wonky die. Once, a guy in my group rolled ~30 1's over a given night. It was ridiculous, like every other roll was a 1. It kept happening even with other people rolling the stupid die. But, because it was for both combat and NWP checks, he wound up being useless in combat, but great in every other way. Which at least made things more interesting than if he suddenly started failing everything.

He doesn't get to roll that die anymore, though.

I mean, my preferred solution is to use bell curve systems, so that a single die has less impact. But different strokes for different folks.

[Lord Torath]

My group never had any problems with THAC0, or descending Armor Class. I guess we intuitively knew that a +X bonus or a -Y penalty was applied in what ever way made it a bonus or a penalty. If you need to roll a 14 or higher, a +4 bonus is applied to your die roll, not your target number. A shield +2 makes you harder to hit, so naturally, you subtract that bonus from your AC, because low ACs are better.

I suspect descending AC is a hold-over from the table-top miniature wargaming rules they were using.

[1337 b4k4]

Incidentally, if your GM is ok with giving out AC numbers (and really they should be because they're hardly secret after 3 rounds). You can turn THAC0 into a static target by moving the AC value to the other side of the equation. So d20+mods+AC >= THAC0 means you hit.

[Jay R]

It's easy, if you are actually trying to learn the new system.

It's confusing if you are trying to think in terms of the old system while using the new one.

[erikun]

A lot of the confusion I've seen surrounding THAC0 involves a lot of shortcuts and confusing (and contradictory) ways of dealing with it. You could see one method of calculating it in a magazine, another in a splatbook, and a third from a friend, and confusing one method with another would turn the entire thing into a giant mess, requiring you to sit down and re-calculate the entire thing from the beginning. It seems especially confusing to people who are familiar with the d20 System and try to translate it.

On the other hand, if you've only been introduced to one way to deal with it, THAC0 works perfectly fine. It also doesn't really need a "translation", as the math works perfectly fine for the one person intended to use it. (the DM) Perhaps the only point of confusing regarding THAC0 and AC is that an Armor +2 has a lower AC than the standard armor, and a Cursed Armor -5 has a higher AC. But that tends to be rather well handled in the AC tables, and most other magical effects that I recall used language like "reduce the AC by two points" to be clear.

[NomGarret]

Having cut my D&D teeth (though not my ttrpg teeth) on THAC0, I agree that while it is not particularly harder, it is less intuitive. I've seen plenty of cases where it and the "is high good or bad" situation is a barrier to new players enjoying the game. I think it comes up as often as it does because it's quick and easy to convey.

[Grumm]

THAC0 is awesome. It is WHY I play AD&D 2e (or at least one of the many reasons).

I always find the "subtraction is difficult!" claim confusing... THAC0 doesn't need to involve subtraction. At my table, I have the players roll a die and add any bonuses that they know of (high strength, magic weapons... etc.) Then on my side of the screen, I ADD the target's AC and see if the total is higher than the character's THAC0. No subtraction necessary. Just think THAC0 as the target number for a character of that level (i.e. a 3rd level Fighter hits on an 18+) and think of the enemy's AC as a modifier to the attack roll (i.e. chainmail gives a +5 to hit and plate mail gives a +3 to hit).

THAC0 is dead simple and it keeps the right amount of info in the players' hands... the players should just be worrying about their d20 roll and their miscellaneous bonuses. As the DM, I just keep a short list for the party's THAC0 scores (i.e. PC#1 18, PC#2 19, PC#3 19 etc.) and the monster's stats handy. Easy peasey. Later editions felt like "roll-playing" games for me because all the modifiers and numbers were shoved in the players' faces 24/7... base attack bonus, ability score modifiers, magic weapon modifiers... you end up with a +22 on a die roll that itself only has 20 sides!

[Knaight]

THAC0 is dead simple and it keeps the right amount of info in the players' hands... the players should just be worrying about their d20 roll and their miscellaneous bonuses. As the DM, I just keep a short list for the party's THAC0 scores (i.e. PC#1 18, PC#2 19, PC#3 19 etc.) and the monster's stats handy. Easy peasey. Later editions felt like "roll-playing" games for me because all the modifiers and numbers were shoved in the players' faces 24/7... base attack bonus, ability score modifiers, magic weapon modifiers... you end up with a +22 on a die roll that itself only has 20 sides!

Unless the players don't know their own THAC0 this leaves exactly the same information in the players' hands as the BAB system. As for the rest of the modifiers, they're not a function of BAB vs. THAC0 in any way.

[MeeposFire]

THAC0 is awesome. It is WHY I play AD&D 2e (or at least one of the many reasons).

I always find the "subtraction is difficult!" claim confusing... THAC0 doesn't need to involve subtraction. At my table, I have the players roll a die and add any bonuses that they know of (high strength, magic weapons... etc.) Then on my side of the screen, I ADD the target's AC and see if the total is higher than the character's THAC0. No subtraction necessary. Just think THAC0 as the target number for a character of that level (i.e. a 3rd level Fighter hits on an 18+) and think of the enemy's AC as a modifier to the attack roll (i.e. chainmail gives a +5 to hit and plate mail gives a +3 to hit).

THAC0 is dead simple and it keeps the right amount of info in the players' hands... the players should just be worrying about their d20 roll and their miscellaneous bonuses. As the DM, I just keep a short list for the party's THAC0 scores (i.e. PC#1 18, PC#2 19, PC#3 19 etc.) and the monster's stats handy. Easy peasey. Later editions felt like "roll-playing" games for me because all the modifiers and numbers were shoved in the players' faces 24/7... base attack bonus, ability score modifiers, magic weapon modifiers... you end up with a +22 on a die roll that itself only has 20 sides!

I have no problem with THAC0 and love AD&D but as a DM and a player this is the sort of way doing THAC0 I could never use. Don't ask me why I cannot tell you but this method always caused me major problems. I am not saying you are wrong just relating about how for me (and others too) that what is easy for one is not easy for another.

[GloatingSwine]

It's not complicated, but it is counterintuitive.

Under THAC0 the target is a property of the actor and the modifiers are a property of the target.

Under BAB the target is a property of the target and the modifiers are a property of the actor.

[hamlet]

It's not complicated, but it is counterintuitive.

Under THAC0 the target is a property of the actor and the modifiers are a property of the target.

Under BAB the target is a property of the target and the modifiers are a property of the actor.

*shrug* So? That's not really all that counter-intuitive, especially if you're looking at it from the point of view that the players are not intended to know the exact to hit numbers that are required to score a hit. They know what they rolled and, in the end, they are told whether or not they succeed or fail, but they do not know by how much either way for that is the provenance of the DM. It's only counter-intuitive if you are working out entirely in the open as became the norm rather than unique in D20.

I still prefer to-hit charts, but that's just me.

[Glorthindel]

Always found it straightforward, and the complaints about it being difficult massively overblown.

Sure, the current system probably works better at first glance under the "bigger number means better" principle, but the actual maths is basically the exact same calculation. Hell, I routinely used 2nd ed adventure modules in my 3rd ed campaign, and converting the Thac0 and AC of the various stat-blocks can be done in your head as you play.

[hamlet]

It's also worth noting that 2nd edition THAC0 can easily (as in within about 3 minutes, the time it takes you to actually type out a couple of sentences) be converted to a BAB system that works perfectly well: believe me, I've done it and played it for near a decade. Don't know if it's "more intuitive," easier, or faster, it just works about as well.

[Knaight]

*shrug* So? That's not really all that counter-intuitive, especially if you're looking at it from the point of view that the players are not intended to know the exact to hit numbers that are required to score a hit. They know what they rolled and, in the end, they are told whether or not they succeed or fail, but they do not know by how much either way for that is the provenance of the DM. It's only counter-intuitive if you are working out entirely in the open as became the norm rather than unique in D20.

I still prefer to-hit charts, but that's just me.

Seeing as AC is hidden information by default, that's not actually a difference in the system.

[tensai_oni]

Sorry peeps, all the explanations that go "Thac0 is simple, you just have to do steps A, B and C and there you have it" do nothing to make it sound any less counter-intuitive. Anyone can grok later editions' to-hit and AC, but this really takes some mental gymnastics to memorize.

Before reading this thread I was convinced that a lot of thac0 fans are just posturing and pretending that anyone who doesn't like the mechanic is just bad at math or dumb in general.

Responses in this thread only further reinforced my opinion.

[Lord Torath]

Sorry peeps, all the explanations that go "Thac0 is simple, you just have to do steps A, B and C and there you have it" do nothing to make it sound any less counter-intuitive. Anyone can grok later editions' to-hit and AC, but this really takes some mental gymnastics to memorize.Seriously????? It is literally (in the definition that means what is said is exactly what is meant) the same calculations involved in BAB. You still have your target number, your situational modifiers, your base modifier, and your die roll. The only difference is the direction of improving armor class. You're still adding or subtracting the same numbers.

It's all there in the acronym: To Hit Armor Class zero(0). If your THAC0 is 15, a roll of 15 hits AC:zero (or AC:20 in the BAB version). A 16 hits AC -1, while a 14 hits AC:1. That's it.

[Anonymouswizard]

Sorry peeps, all the explanations that go "Thac0 is simple, you just have to do steps A, B and C and there you have it" do nothing to make it sound any less counter-intuitive. Anyone can grok later editions' to-hit and AC, but this really takes some mental gymnastics to memorize.

Before reading this thread I was convinced that a lot of thac0 fans are just posturing and pretending that anyone who doesn't like the mechanic is just bad at math or dumb in general.

Responses in this thread only further reinforced my opinion.

Meanwhile, posts like this reinforce my 'people who don't like THAC0 are lazy' view.

I mean, if it's really too much of a problem to do THAC0-(1d20+modifiers)=AC hit, you can spend like 2 minutes turning it into a to-hit table. I mean, it is slightly counter intuitive, but no more than GURPS and it's 'roll under skill to succeed'. No mental gymnastics required, just a requirement to do some basic maths.

Now THAC0 is also slightly slower than BAB, in that most people add faster than they subtract, but not significantly so. But if you want to skip that at level one write up a to-hit table and adjust it whenever your THAC0 changes.


FWIW I never liked 'THAC0 is target number', although I understand it, because once grokked subtracting your attack roll from your THAC0 is slightly faster. But it's not hard.

(Plus let's take the challenge of changing it to a positive bonus. AC is now equal to 20-oldAC, your accuracy bonus begins at 0 and increases as THAC0 would decrease. One minute and done, although you might want to type out the new accuracy bonus tables for classes.)

[D+1]

It's neither complicated OR counter-intuitive. We were using that and other simple shortcuts to the attack matrices of 1E long before 2E came out. I have to assume that those who have problems with understanding it either just don't like it PERIOD (for whatever reasons) and therefore try to label it in order to justify their dislike, or else they simply had it very badly explained to them. It ain't just simple addition, but neither is it calculus.

[Digitalelf]

We were using that and other simple shortcuts to the attack matrices of 1E long before 2E came out.

Just a minor nit-pick, but saying "long before 2e came out" implies (to me at least) that you mean to say that THAC0 is a 2nd edition rule.

THAC0 was first introduced to 1st edition in 1983 with the module "UK3: The Sentinel" as an optional rule. It actually appeared much earlier in an issue of "White Dwarf" Magazine but I am only referring to "official" TSR publications.

It latter appeared as an "official" part of the 1st edition ruleset in 1986 with the publication of the "Dungeoneer's Survival Guide" hardbound.

The term THAC0 (as opposed to a usable game mechanic) is actually much much older, and can be found in the 1st edition DMG (published in 1979) on pages 196 - 215 in the "APPENDIX E: ALPHABETICAL MONSTER LISTING".

[Magua]

FMPOV, the stream of this thread is:

1. "THAC0 is not counterintuitive."
2. "I find THAC0 to be counterintuitive."
3. "You're dumb/lazy."

[MeeposFire]

It's neither complicated OR counter-intuitive. We were using that and other simple shortcuts to the attack matrices of 1E long before 2E came out. I have to assume that those who have problems with understanding it either just don't like it PERIOD (for whatever reasons) and therefore try to label it in order to justify their dislike, or else they simply had it very badly explained to them. It ain't just simple addition, but neither is it calculus.

It is only complicated actually when people try to simplify it (though to be fair for some who do that it makes it easier to use despite the extra complications they add to it) however it is certainly less intuitive than rolling a number and adding a bonus to it. You can find studies that discuss how subtraction is less intuitive than addition even if it really should be just as easy. Now I do agree that there are a lot of people (especially those who have not really played with it) that make a much bigger deal than it is because it really is not that hard but to declare that it is as intuitive as addition is going too far the other way.

Now it does have one advantage not being talked about right now which is that it usually deals with smaller numbers. Addition is relatively easy but the bigger numbers get the less easy it becomes. THAC0 does tend to revolve around smaller numbers and that is a bonus though it does lose points again due to quickly involving negative numbers which once again are not as easy to use for many people.

[Knaight]

It's neither complicated OR counter-intuitive. We were using that and other simple shortcuts to the attack matrices of 1E long before 2E came out. I have to assume that those who have problems with understanding it either just don't like it PERIOD (for whatever reasons) and therefore try to label it in order to justify their dislike, or else they simply had it very badly explained to them. It ain't just simple addition, but neither is it calculus.

Complicated and counter-intuitive aren't absolute terms - they're relative to other things. Compared to BAB it is both complicated and counter-intuive. Compared to the attack matrices it's simple and intuitive. Compared to the Burning Wheel Fight! Matrix it's amazingly simple and highly intuitive. Compared to opposed combat skill rolls (which show up in a lot of systems) it's not particularly complicated and a bit counter-intuitive, although those systems then tend to introduce additional complications.

[2D8HP]

...I still prefer to-hit charts, but that's just me.


Your not alone, I prefer the "To Hit" Tables (or the "Attack Matrix" charts) as well.

Though why did you need to roll a 17 in oD&D to hit a man with "Plate Armor & Shield" but an 18 in 1e AD&D to hit a man with "Plate mail & shield" (both AC 2), and why no armor was AC 9 in oD&D, but AC 10 in 1e AD&D confused me, among other things.

Anyway, THAC0 and BAB don't seem very different to me, but I never played 2e, just 0e/1e, and I relied on the charts on the backside of my Dungeon Masters Screen.

http://www.waynesbooks.com/images/graphics/1stedadd2ndprtscreens.jpg

[spinningdice]

I don't have a problem with the maths involved, but I find it annoying that bonuses are still expressed as + and penalties as -, even though they do the opposite (some members of our group prefer the older games so I play AD&D2e quite often).

Apparently the Armour Class came from naval wargaming, where ships were described as having First Class armour, or second class armour etc. at least so I've heard.

It's not half as annoying as having to constantly work out what your initiative is depending on what spell you want to cast, or weapon you want to use...

[hamlet]

Your not alone, I prefer the "To Hit" Tables (or the "Attack Matrix" charts) as well.

Though why did you need to roll a 17 in oD&D to hit a man with "Plate Armor & Shield" but an 18 in 1e AD&D to hit a man with "Plate mail & shield" (both AC 2), and why no armor was AC 9 in oD&D, but AC 10 in 1e AD&D confused me, among other things.

Anyway, THAC0 and BAB don't seem very different to me, but I never played 2e, just 0e/1e, and I relied on the charts on the backside of my Dungeon Masters Screen.

http://www.waynesbooks.com/images/graphics/1stedadd2ndprtscreens.jpg

They rescaled the AC scales slightly between the two games. One started at AC10 the other at AC9. Thus, the difference.

[Khedrac]

They rescaled the AC scales slightly between the two games. One started at AC10 the other at AC9. Thus, the difference.

They also left an armor type out of BECMI (though off hand I don't recall which) hence plate + shield ends up at AC2 in both systems...

[MeeposFire]

They also left an armor type out of BECMI (though off hand I don't recall which) hence plate + shield ends up at AC2 in both systems...

I believe there is no padded armor since AC 9 is not needed in BECMI.

[D+1]

Just a minor nit-pick, but saying "long before 2e came out" implies (to me at least) that you mean to say that THAC0 is a 2nd edition rule.
Nope. Not what I mean at all. I mean 2nd Edition only took a common house rule and stamped it as official.


THAC0 was first introduced to 1st edition in 1983 with the module "UK3: The Sentinel" as an optional rule. It actually appeared much earlier in an issue of "White Dwarf" Magazine but I am only referring to "official" TSR publications.

It latter appeared as an "official" part of the 1st edition ruleset in 1986 with the publication of the "Dungeoneer's Survival Guide" hardbound.

The term THAC0 (as opposed to a usable game mechanic) is actually much much older, and can be found in the 1st edition DMG (published in 1979) on pages 196 - 215 in the "APPENDIX E: ALPHABETICAL MONSTER LISTING".
My point being that even before realizing that there was a useful column in the back of the DMG listing of monster stats that was labeled "To Hit A.C. 0" we understood that we did not need - and did not want - to repeatedly check against charts to see what we needed to hit. We took the column of the appropriate chart for our characters class and level and wrote it out on our character sheets. Once in a while a player would just shorten that to the score needed to hit AC 0 and adjust for the actual AC once they knew what it was. We UNDERSTOOD that the attack matrices were cumbersome and so naturally sought out shortcuts. We did not have to stumble across a particular module, buy the Dungeoneers Survival Guide, or have someone point out the column in the DMG. We figured out what we needed and could use on our own. We similarly did not have to wait for a Dragon magazine or White Dwarf article, or actual 2nd Edition formal core rules to introduce the idea. it was the sort of thing found in EVERY RPG outside of D&D. D&D, simply by virtue of being the oldest and the 800 pound gorilla, was merely slow to make the change already in place as house rules. "Thaco" was in use LONG before then and not just by our gaming group but by a lot of gamers. It did not require a lot of perceptiveness or ingenuity to see the "problem" and make a solution happen. Even after switching to 2E the character sheets I was designing for our particular group needed no change to accommodate thaco and never did. I simply kept the same line listing AC's from +10 to -10 and players filled it in after looking up thaco instead of looking up the line of the correct attack matrix, thus still retaining an improvement over just listing THACO because the extra step of adjusting for ACTUAL AC was already done on everyone's character sheet.

I'm just saying that "thaco" is not rocket science no matter how you slice it and where it first appeared in print is no more than a geeky trivia question answer. It was a reasonably widely utilized idea spontaneously put into action all over as a shortcut/replacement to the original D&D attack matrices.

[Digitalelf]

Nope. Not what I mean at all.

Fair enough. I did say that was how I interpreted your meaning.

Thank you for the clarification. :smallbiggrin: