#thac0

[tireddungeonmaster]

Just need to see if my mom's opinion on THAC0 is as unpopular as I think

[shaneplays]

Before TSR published a Dungeons & Dragons character sheet the fan community stepped in, with the first fan-created sheet appearing in Stephen Tihor's Haven Herald fanzine in May 1975 and Alarums & Excursions publishing Jack Harness's character sheet in July. Soon after Wee Warriors released the first commercially available D&D character sheets with the Character Archaic, which was distributed but not published by TSR. In 1977, TSR finally published its first character sheets. Important record keeping… on THAC0 Thursday!!

[randomtangle]

THAC0 Thursday: THAC0

Time to explain THAC0! It’s quite simple, really.

First, what does it mean? THAC0 stands for “To Hit Armor Class Zero”, and it’s exactly that. What you need to roll to hit a target with an armor class of 0.

From this, you do a little math to find out what you need to hit a target with a different armor class. The equation is simple:

THAC0 - AC = x

So, if you have a THAC0 of 20, and they have an AC of 8, you need to roll a 12. This works for negative AC as well since you just subtract a negative, which is the same as adding its inverse, so if you have a THAC0 of 15 and they have an AC of -3, you need to roll 18 to hit.

That’s it! That’s all there is to THAC0! It’s not that complicated.

Thank you for reading! Hope you enjoyed!

[3d34-2]

[hiscursedness]

Dinosaur dungeon masters have a THAC0mizer

[xain-russell]

I just learned about THAC0 and I am so glad I started playing D&D after they tossed that in the garbage can. Decades of jokes about too much math in D&D suddenly make a lot more sense.

[eigwayne]

THAC0 For Dummies

Alrighty gentle readers, today we’re going to learn about THAC0! Because I’m still annoyed someone tried to talk about the history of D&D combat without even attempting to understand what it was. Is it an over-complicated method? Yes. Did anyone actually like it? No. But THAC0 was what we had at the time. And if you present yourself as an authority, you have to make an effort.

And I’m going to make it as low effort for YOU as I can. My qualifications? I started playing with 2e, played for some years, DMed on and off, and taught several people how to play, all in Second Edition. And I have a nice cheatsheet of reminders left from those days ^_~

What the Hack is THAC0?

“THAC0″ is short for “To Hit Armor Class Zero” and you usually say it “thacko”. It was how you calculated whether your attack hit the target in Second Edition D&D. You wanted both your Armor Class and THAC0 to be low in 2e, so AC 0 or below was the goal (yes, you could go below zero).

I found the easiest way to teach what THAC0 was is to call it “To Hack-o”, because that’s what it was usually used for: hacking at stuff.

Actually finding out your THAC0 was a chart. When you set up your character, you checked this bad boy, found your class and level, and noted the number (there was a second chart with a shorthand of the THAC0 progression and that was more confusing, so just use the one below). You calculated it during character creation but the chart wasn’t until several chapters later, so that was a pain in the butt, but the chart itself is fairly straightforward.

Some things could lower this (remember, lower is good!), and basically you calculated your base THAC0, applied any bonuses from Strength or magic weapons, etc., and there you were. You could encounter things to penalize or apply bonuses your THAC0 or opponents’ AC during play, but that’s beyond the scope of this article.

To actually hack-o, you rolled a d20, applied any bonuses if necessary, and subtracted that from your THAC0. The result was the AC you hit with that blow. If the target’s AC was equal or higher, you hit it, if it was lower, you didn’t. The DM would calculate that part, though, so players typically didn’t have to worry about it.

Examples:

example: d20 Roll is 10, no bonuses            A. THAC0 20 – 10 = hit AC 10            B. THAC0 17 – 10 = hit AC  7            C. THAC0 10 – 10 = hit AC  0            D. THAC0 5   – 10 = hit AC -5

If opponent’s AC is 8: A fails but the others succeed. If opponent’s AC is 3: C and D succeed, but A and B do not. If opponent’s AC is -3: D succeeds but A, B, and C do not.

example: THAC0 is 5           E. 5 –  2 = hit AC  3           F. 5 – 10 = hit AC -5           G. 5 – 18 = hit AC -13

If opponent’s AC is 3 or above: G, F, E all succeed. If opponent’s AC is -3: G and F both succeed, but E fails

In summary:

THAC0 = “To Hit Armor Class 0 (zero)” = To Hack-o = How Good You Hit Stuff

In Second Edition, you want LOW numbers for THAC0 and AC, and HIGH numbers for the attack roll.

To attack using THAC0:

THAC0 – d20 = lowest Armor Class you could hit, DM calculates the rest. (hit chance – attack roll = armor class hit)

If opponent’s AC is higher than above, you hit. If opponent’s AC is lower than above, you miss.

That’s it. THAC0 is not some inscrutable demonic equation. What makes it annoying and complicated is the language, and that you wanted THAC0 and AC to be low but the attack roll to be high, so you had to adjust your mental train partway through the calculation. The calculation itself? Is just subtraction.

[uncleasriel]

I find thinking about THAC0 and descending AC as the Vulnerability Window. As Base AC goes down, it's the number of Weak Spots that are open to attack. Conceive of it like that and understanding begins to flow

I gave b/x a look because of your posts and you are right that most mechanics are simpler than 5e but I don't think I can get into it because of the weird armor mechanics. I don't understand why armor reduces your AC? And having to compare the enemy's AC with a table for every attack roll seems just really clunky and compplicated

Okay fair. The Attack Matrix and descending AC are one of those things that can look really clunky and create culture shock when you're used to modern D&D's mechanics.

They're not really that complicated tho, I'll try to explain.

B/X, like all old-school editions of D&D, uses descending AC, which means that lower AC values are better. Lower AC makes you harder to hit, higher AC makes you easier to hit (as opposed to modern D&D's ascending AC, where higher values are better) That's why armor makes your AC lower rather than higher.

The Attack matrix mechanic is kinda clunky, but the only value from it you actually need to know is the roll needed to hit AC 0. As long as you know that value, you can find the attack roll needed to hit any AC by subtracting the enemy AC from the To-hit-AC-0 value.

Let's see an example.

Let's say you have a level 4 fighter. According to the attack matrix, to hit an enemy with AC 0 you need 17 or more on your attack roll. That's the only value you need to know. When fighting an enemy with any other AC, you can subtract their AC from 17 to find out how high you need to roll. So for example, if you're trying to hit an enemy with AC 4, then 17-4 = 13, you need an attack roll of 13 or more to hit them. If you're fighting an enemy with AC 6, then 17-6 = 11, you need to roll 11 or more to hit them.

That's why both AD&D editions opted to do away with the attack matrix and instead just give you the value of your THAC0 (To Hit AC 0), since all other to-hit rolls can be calculated from it.

Now, of course, if you're used to the way ascending AC works in modern D&D, that might still seem a little unintuitive for you. Luckily there are several B/X-based retroclones that do away with the mechanic entirely and make it work like in modern D&D instead, so you might want to check those out.

Old-School Essentials is extremely faithful to most of B/X's mechanics, but it has ascending AC as an optional mechanic.

Basic Fantasy is mostly B/X-based but it modernizes a few mechanics, including doing away with descending AC entirely and using ascending AC instead.

[ramavoite]

[avinox]

I feel so bad for those who haven't played the original Baldur's Gate, they don't know that THE LORD OF MURDER SHALL PERISH, BUT IN HIS DOOM HE SHALL SPAWN A SCORE OF MORTAL PROGENY. CHAOS WILL BE SEWN FROM THEIR PASSAGE. SO SAYETH THE WISE ALAUNDO

[shaneplays]

This THAC0 Thursday absolutely has to be dedicated to James M. Ward, whose recent passing surprised and saddened the RPG community. Among many accomplishments in the industry, James created Metamorphosis Alpha (the first published science fiction RPG) which was released from TSR in 1976. He wrote the game after urging Gary Gygax to make a sci-fi version of D&D, to which Gary replied "I don't have time, but why don't you do it?" Challenge accepted! He was also instrumental in the creation of Gamma World, which many think of as the planet-based Metamorphosis Alpha. James M. Ward: An RPG legend gone, an RPG legend remembered… on THAC0 Thursday!!

[destronlok]

I played an RPG recently that used a universal chart for task resolution. Players had to consult a chart to attack in the same way they might in a game with descending AC.

That got me thinking, maybe they'd be fine playing in a game with descending AC.

“Ascending armor class better represents the normal human experience!” No, you’re just more used to it. And both scales arbitrarily set 10 at “no armor or shield” anyway.

[thetavolution]

More tweets re-attributed to BG3 characters.

I also did some for my Tavs.

Also I HAD planned to romance someone new on my gith paladin, Vaira, but I couldn't help it.

She fell for Gale lmao.

She also became besties with Lae'zel.

[y-rhywbeth2]

There is a scale of tolerance in ttrpg players regarding how much maths and bookkeeping they'll do.

On one end is the player who copes best with the bare bones of the World of Darkness. As in basic mortals, vampires if you stretch. All they have to do, for the most part, is count dots. More maths than that causes distress.

On the other end is the maths nerd who wants you to port THAC0 into 5e rules and is in utter dismay that DnD is apparently decreasing the amount of numbers they need to juggle.

[battlfofendorr]

Do you think Adrian Chase was team THAC0, when he played D&D? Or do you think he clung to the latest and coolest, and printed out all the errata for best min-maxing?

[stickygallery]

drawinnn

Gonna keep working on the owl dragon plan, but my wrist has very low HP