Help me understand THAC0

I'm pretty sure I get it, but this chart is throwing me off (It's from OSRIC, if that is important).
As I understand it is supposed to work like
>[THAC0] - [Dice Roll] = AC hit
And THAC0 descends with class + level.
This makes sense.
But, how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)? And why is there the string of 20s in the chart, is this just a buffer to help the player?

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  1. 1 month ago
    Anonymous

    Grogs will seriously insist on referencing a chart instead of being able to just do the math on the fly because Old Good New Bad.

    • 1 month ago
      Anonymous

      No, it's because standardization is a spook to them. Too much of OSR design relies on bespoke jank to crowbar into a single resolution mechanic without a truly obscene workload, and the attempt Wizards of the Coast made of this with 3e left a sour taste in the mouths of enough people to create a meaningful market niche.

      • 1 month ago
        Anonymous

        They so badly want to be transported back to the era where RPGs were these esoteric tomes that they had to puzzle out and struggle to understand until they'd give up and make their own rules and feel so accomplished and intelligent for coming up with a more elegant solution than whatever the middle aged nerds who wrote the book published.

        • 1 month ago
          Anonymous

          That may be a thing for the Ur-Grogs, but speaking as a 3.5aboo I perfectly well understand the want for Thing A and Thing B working in different ways. Just... Not for core resolution mechanics, that makes the learning experience a mess.

    • 1 month ago
      Anonymous

      Both THAC0 and the traditionally used attack matrix are dumbed down versions of the genuine autistic table that was in Chainmail. You know, the rules you were assumed to be using in conjunction with OD&D but less than 10% actually did.

      • 1 month ago
        Anonymous

        >2h sword kills easier through armor
        What in the goddamn

        • 1 month ago
          Anonymous

          Makes sense. The armoured target is less agile and thus easier to hit, and the 2-handed sword doesn't give a shit about armour.

    • 1 month ago
      Anonymous

      Frick you, D&D was created by atuards and to autards charts are fun.

      https://i.imgur.com/MIzZcid.png

      I'm pretty sure I get it, but this chart is throwing me off (It's from OSRIC, if that is important).
      As I understand it is supposed to work like
      >[THAC0] - [Dice Roll] = AC hit
      And THAC0 descends with class + level.
      This makes sense.
      But, how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)? And why is there the string of 20s in the chart, is this just a buffer to help the player?

      You use the table. Linear math for attack progression doesn't exist until AD&D2E.

      You could also do:
      >THAC0-AC=<[Dice Roll] hit
      Works better in my brain that way.

      >Works better in my brain that way.
      Works better for everybody who doesn't have a case of Gygax-brain. Normal people want to know the target number they're rolling for, subtracting the total of the die after you roll it is ass backwards.

      If a little bit of subtraction filters you that hard, you don't deserve to have fun.

      • 1 month ago
        Anonymous

        >filtered by subtraction
        [THAC0 - AC = d20 roll to hit] gives the same answer. This seems like the way everybody would do it so they know what number they're rolling for.
        The "official" way of calculating it [THAC0] - [Dice Roll] = AC hit, is the tard-friendly way so players don't have to do something crazy like subtract a negative number for ACs below 0.

        • 1 month ago
          Anonymous

          >TELL ME THE MONSTER AC!!!!
          No. Just do the on the fly math as intended you moron.

        • 1 month ago
          Anonymous

          >This seems like the way everybody would do it so they know what number they're rolling for.
          Players are not entitled to this information, since this information may give away important clues in non-standard scenarios with unusual factors. It's a game, you're supposed to use your fricking brain not be spoonfed.

    • 1 month ago
      Anonymous

      The bad-at-maths generation is not the grognards. D20 moved away from ThAC0 because newer players couldn't handle subtracting negatives in their head to derive the target number. Instead of referencing charts (or grappling with 5th grade mathematics) they just reversed the direction of AC to get rid of negatives and move the maths level down to first grade instead.

      • 1 month ago
        Anonymous

        >he thinks subtraction is more difficult
        Brainlet

    • 1 month ago
      Anonymous

      >because Old Good New Bad
      How the frick is that their fault?

    • 1 month ago
      Anonymous

      I like to do both

    • 1 month ago
      Anonymous

      You're literally too stupid for descending AC which is even simpler mathematically than the unnecessary adding on every roll of ascending.

    • 1 month ago
      Anonymous

      It's actually really funny how dumb they are when they try to act smarter than you.

      • 1 month ago
        Anonymous

        You would know, huh

  2. 1 month ago
    Anonymous

    Charts aren’t hard to use and with the way many RPG manuals are written I would say they are necessary. I hate to have to argue the point with someone who wants to contest it by reading along with him. Charts mitigate this and make better systems tbh

    If you say charts are hard to use I question either your intelligence or your integrity because they are not hard to use and usually mean the system is better designed really

  3. 1 month ago
    Anonymous

    THAC0 is probably one of the worst-conceived components of any mainstream RPG. You're better off not learning any system that uses it.

  4. 1 month ago
    Anonymous

    You could also do:
    >THAC0-AC=<[Dice Roll] hit
    Works better in my brain that way.

    • 1 month ago
      Anonymous

      Oh neat.
      How am I supposed to know the THAC0? Is it listed somewhere?

      • 1 month ago
        Anonymous

        I think it is supposed to be listed in your class tables. Something like BAB. Rules Cyclopedia also recommends to have a list of of a handful of common AC at ready so you won't have to subtract each time.

        • 1 month ago
          Anonymous

          Thank you!

          • 1 month ago
            Anonymous

            Oh neat.
            How am I supposed to know the THAC0? Is it listed somewhere?

            Animebrain moron posters like you shouldn't be here

            • 1 month ago
              Anonymous
    • 1 month ago
      Anonymous

      >Works better in my brain that way.
      Works better for everybody who doesn't have a case of Gygax-brain. Normal people want to know the target number they're rolling for, subtracting the total of the die after you roll it is ass backwards.

  5. 1 month ago
    Anonymous

    Think of it like this:
    Your THAC0 is the DC of your attack roll.
    Your enemy's AC is the bonus on your attack roll.

    In modern D&D, we're used to the bonus on the attack roll coming from the skill of the attacker, and the target number or DC of the attack roll living in the defender's armor and ability to dodge. 1d20 + bonus from attacker skill vs. target number based on defender's defenses.

    In old-school D&D, you can conceive of the descending AC mechanic in exactly the same way, merely by reversing where the attacker skill and the defender's ability to avoid damage "live." 1d20 + a bonus that lives in the defender's armor (i.e., you can conceive of descending AC as a "vulnerability" stat, where AC 10 is highly vulnerable, AC 0 is not that vulnerable, AC −10 is nigh invulnerable, and this manifests as an armor-based bonus you grant your enemy to hit you) vs. a target number that lives in the attacker's skill, i.e., your generic "DC to hit anything" starts high, at 20 or 19, and goes down as you become a better fighter.

    THAC0 is literally just a DC.

    • 1 month ago
      Anonymous

      Thank you! I didn't make the connection between THAC0 and the rest of old school having class-based DCs, so that makes a lot of sense.

      >But, how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)?
      It's just the "AC 0" column on the attack table. If you'd rather calculate it, it varies by edition.
      • In AD&D, everyone starts at THAC0 20. Fighters (and cavaliers) improve 1 point per level, clerics (and monks if you're playing 1e, where monks aren't a cleric sub-class) 2 points per 3 levels, thieves (and psionicists) 1 point per 2 levels, and magic-users 1 point per 3 levels. The 1e attack tables don't quite line up with that, but the differences are minor and unimportant; if you use the 2e THAC0 chart, you'll be fine.
      • In BECMI, fighters improve 2 points per 3 levels, clerics and thieves 2 points per 4 levels (which you can reduce to 1 point per 2 levels if you like), and magic-users 2 points per 5 levels. BX and 3LBB go a bit faster than this because of a few 3-point jumps at specific levels; if you want a BX accurate THAC0, use OSE or calculate it yourself.
      • If you want to smooth out the progression so that there are never any jumps larger than 1 point, you can do that. It's cool.
      >And why is there the string of 20s in the chart, is this just a buffer to help the player?
      Edge cases that come up so rarely that they don't matter. Feel free to ignore. Just have a nat 20 always hit and a nat 1 always miss.

      Thank you so much! The exceptions were throwing me off, so it's good to know they were just that.

      • 1 month ago
        Anonymous

        i would clarifiy that you shouldnt ignore the reoccuring 20's, there is a reasons for them to do with mass battle, but seeing as new school players dont do war scenarios, its no surprise they would be removed

        the other way of thinking about it, is that as the base Thac0 is 20, the normal hit rate is 5%, AC 0 is a fully armoured man (full plate plus shield) and thus what the enginge is balanced around. AC 10 is the default in modern d&d, because in od&d and 1e, you get a +10 to hit an un-armoured target, +5 to hit chainmail compared to your base thac0, which is what the chart shows etc, thats why low good
        a magic user with 10AC is not base AC, he is a collosal vulnerability.
        overworld kobolds for example, come in groups of 40, (40-400, 1d10x40 originally, corrupted to 4d10 x10 in bx); assuming a party of fighting men in full armour, there is a 5% hit rate*, so two (1d4 damage) attacks will typically hit, and the bell curve means that combat is very unswingy and very consistent, a fighting man in old d&d being able to make one attack per round per level, a party of five lvl4s, would roll 20 attacks per round back, with their modifiers up to half these attacks will likely hit and kill so you get some very consistent results as to what you can maintain. for 10 of the kobolds to hit in a round and cause an unexpected result, its 1 in 20 ^of whatever infinitely small number. likewise goblins in 30-300, but they do 1d6 damage, etc
        the AC system breaks down when you lower the number of combatants and set the normal hit rate at around 50%, and only give 1 attack per round, plus maybe a second at some point; results in some very unsatisfying swingy rounds
        *flanking for kobolds thus becomes very important, to get a +2 for partial flanking triples output, +4 for full flanking quintuples it
        (the table only goes to -10, because originally +5 shield and armour was the best possible until powercreep added +6 magic later on, so AC 0, with a magic modifer of 10)

        • 1 month ago
          Anonymous

          > mass battles
          I noticed that monsters came in huge numbers, but I didn't realize the party was meant to solo them (plus hirelings I guess). Though HP pools seem a lot smaller than 5e, so this makes sense.

  6. 1 month ago
    Anonymous

    >But, how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)?
    It's just the "AC 0" column on the attack table. If you'd rather calculate it, it varies by edition.
    • In AD&D, everyone starts at THAC0 20. Fighters (and cavaliers) improve 1 point per level, clerics (and monks if you're playing 1e, where monks aren't a cleric sub-class) 2 points per 3 levels, thieves (and psionicists) 1 point per 2 levels, and magic-users 1 point per 3 levels. The 1e attack tables don't quite line up with that, but the differences are minor and unimportant; if you use the 2e THAC0 chart, you'll be fine.
    • In BECMI, fighters improve 2 points per 3 levels, clerics and thieves 2 points per 4 levels (which you can reduce to 1 point per 2 levels if you like), and magic-users 2 points per 5 levels. BX and 3LBB go a bit faster than this because of a few 3-point jumps at specific levels; if you want a BX accurate THAC0, use OSE or calculate it yourself.
    • If you want to smooth out the progression so that there are never any jumps larger than 1 point, you can do that. It's cool.
    >And why is there the string of 20s in the chart, is this just a buffer to help the player?
    Edge cases that come up so rarely that they don't matter. Feel free to ignore. Just have a nat 20 always hit and a nat 1 always miss.

  7. 1 month ago
    Anonymous

    Do you say THAYco or thACKo?

    • 1 month ago
      Anonymous

      th'coeur, in a french sorta way

    • 1 month ago
      Anonymous

      thayce-zero

    • 1 month ago
      Anonymous

      Taco. Like the mexican food.

    • 1 month ago
      Anonymous

      "How now, brown drown?" said the liches with stitches in their britches, while goblins gobbled gobbledyasiatic and kobolds cobbled cobblestones. "We say 'THAC0' to the Draco here in Waco."

    • 1 month ago
      Anonymous

      >thACKo
      That. Because it sounds like taco.

    • 1 month ago
      Anonymous

      Thay-co.

      • 1 month ago
        Anonymous

        Based Midwesterner.

        THACK-oh

        Coastal Degenerate.

    • 1 month ago
      Anonymous

      THACK-oh

    • 1 month ago
      Anonymous

      Taco

  8. 1 month ago
    Anonymous

    Zoomers will literally look at a list of attack roll DCs and make up excuses to not be able to use it.

  9. 1 month ago
    Anonymous

    >But, how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)?

    You need to look it up, no other way.

    ...Which is true of attack bonus progression in most games anyway.

    >And why is there the string of 20s in the chart, is this just a buffer to help the player?

    Yes. It's there so that you have some tiny chance of hitting monsters that are too high level for you.

    IIRC it doesn't show up in every version.

    • 1 month ago
      Anonymous

      Makes sense.

  10. 1 month ago
    Anonymous

    >I'm pretty sure I get it, but this chart is throwing me off
    It would do. Charts like that are what THAC0 was introduced to replace, making it simpler to calculate on the spot using only your character sheet.

  11. 1 month ago
    Anonymous

    thac0 is easier to understand when you remember that it stands for "to hit ac 0." if your thac0 is 16 and your enemy has 0 ac then you need a 16 to hit. if the enemy has 5 ac then you subtract 5 since lower ac is better and only need 11 to hit. if the enemy has -2 ac then you add and need 18 to hit.

  12. 1 month ago
    Anonymous

    Black person, did you check your character sheet? You either do the math in your head or you check the table on your character sheet. Pic related, grabbed it at random.

  13. 1 month ago
    Anonymous

    Your thac0 minus their ac = target number

    How is that so hard?

    • 1 month ago
      Anonymous

      I didn't know how to find the thac0, but I have found it 🙂

      • 1 month ago
        Anonymous

        Oh sry

  14. 1 month ago
    Anonymous

    It is a terrible combat resolution system, but if you are so fricking stupid that you can't figure it out, you literally don't deserve to play the game

  15. 1 month ago
    Anonymous

    >how do I know the THAC0 of a class
    Depending on edition (or boxed set if you're going by basic D&D) every class' THAC0 improves at a different rate and caps out at a different number. The only constant seems to be the Fighter's THAC0 improving at a rate of 1 per level and capping out at 1. That being said, thieves' THAC0 tends to improve at a rate of 1 per two levels, magic-users' at a rate of 1 per three levels, and clerics' at a rate of two every three levels. The caps for these tend to vary between editions/boxed sets and the rate might slow at higher levels.

    • 1 month ago
      Anonymous

      >The only constant seems to be the Fighter's THAC0 improving at a rate of 1 per level.
      Not even that is true, fighters have a staggered progression of -2 every 3 levels in OD&D and Basic because Gary's typewriter was insufficient for making better tables and Basic stuck with the values.

  16. 1 month ago
    Anonymous

    Done

    • 1 month ago
      Anonymous

      >people would rather do all of that than just do some basic math

    • 1 month ago
      Anonymous

      >how ancient is your system, exactly?

  17. 1 month ago
    Anonymous

    I don't understand how anyone can like THAC0 it just tells me everyone here is a /nogame/r and they spend more time flipping through PDFs of rulebooks and not enough time actually reading and playing them.

    T. played adnd 2nd edition the day it came out and still play it today. no i dont use asecending ac because why I bother? once you get into the grove of minus'ing instead of plus'ing it do't matter no mo'

    • 1 month ago
      Anonymous

      >how anyone can like THAC0
      I don't think nobody likes, they bear with it for retrocompatibility reasons (running/using old materials) while also referring to some inherent perks like a functional bounded accuracy and mass combat rules (if i remember correctly there was a rule for defining how many strikes a unit does without having to roll based on the thac0 value of something along the line, i never bothered to check that though so i can't confirm)

    • 1 month ago
      Anonymous

      You wish you knew what the frick you're blathering on about, you imbecilic mongoloid

    • 1 month ago
      Anonymous
  18. 1 month ago
    Anonymous

    ThAC0 is so easy to explain if you can do simple addition and subtraction. Let's just get your scale going first. AC is measured from 10 to -10, 10 being the worst AC and -10 being the best (it can go further than -10, rarely, but for simplicity's sake we are just going to deal with the standard array). Still with me? If so, I will continue

  19. 1 month ago
    Anonymous

    >muh charts bad

    Frick Zoomers hate reading don't they

  20. 1 month ago
    Anonymous

    >combat resolution system requires the players know their target's stats
    Lol.

    • 1 month ago
      Anonymous

      It doesn't. You announce what ac you have got, it doesn't mean you hit it.

      >I hit ac -2
      >"Miss"

      Moron

      • 1 month ago
        Anonymous

        That's even worse lmao. What an awful system. Imagine defending this.

        • 1 month ago
          Anonymous

          Tell us you've never played an RPG without dating you've never played an RPG

          • 1 month ago
            Anonymous

            Shut up. I really don't care. THAC0 is laughably bad design. If you disagree you're simply blinded by nostalgia.

            • 1 month ago
              Anonymous

              >THAC0 is laughably bad design
              Prove it without jerking off your opinion, gamelet.

              • 1 month ago
                Anonymous

                It's inelegant. To facilitate play the players need meta knowlege, or the DM needs to constantly refer to the THAC0 of each player, or the players need to refer to a chart. And for what? It's just a roundabout way of achieving exactly what ascending AC achieves. Yet you cling to it.

              • 1 month ago
                Anonymous

                >Opinion words on top of opinion words.
                You failed.

              • 1 month ago
                Anonymous

                If you say so. I know using it gives you fuzzy warm feelings and that's fine.

              • 1 month ago
                Anonymous

                Your three examples are incorrect. You have to, as DM, keep up with one number. One: the target AC that is needed to hit. Just saying your a fricking moron and move on to a different game, something like tiddlywinks. That's more your speed. We're laughing at you

              • 1 month ago
                Anonymous

                >doesn't know what OR means

              • 1 month ago
                Anonymous

                You still listed three examples regardless of your stupid grammar, moron and all three are erroneous and misleading so just stfu already. You lost the argument, now sit down, little kid. The adults are talking now

              • 1 month ago
                Anonymous

                >or
                >stupid grammar
                Maybe you need a reference chart for the English language?

              • 1 month ago
                Anonymous

                Grammar is language usage, not just spelling, you feckless b***h

              • 1 month ago
                Anonymous

                Unfortunately you forgot to use a full stop at the end of that sentence so your opinion is rendered invalid. I'm sure you can find a handy chart online.

              • 1 month ago
                Anonymous

                Not using punctuation invites discourse but you wouldn't know that because your a moron (insert period here) homosexual

              • 1 month ago
                Anonymous

                >your

              • 1 month ago
                Anonymous

                *you're

              • 1 month ago
                Anonymous

                >To facilitate play the players need meta knowlege, or the DM needs to constantly refer to the THAC0 of each player, or the players need to refer to a chart.

                If you're doing the equation the standard way (THAC0 - target AC = target number needed to hit), the players do need to know their target's AC. But it's also commonly resolved like: THAC0 - die roll = AC or higher/worse you hit. In that case, if your character has a THAC0 of 19 and rolls a 17, you can just call out "I hit AC 2", and the DM can tell you whether you hit your target based on their AC (which he may not have let you know).

              • 1 month ago
                Anonymous

                That makes sense, but in doing so mimics the procedure of resolving ascending AC only less intuitively. What's the benefit of this system?

              • 1 month ago
                Anonymous

                Oh, I'm not here to sell THAC0. THAC0 is perfectly workable, and not something that should ever be a sticking point, but it's a little wonky compared to ascending AC. What I don't love about THAC0/descending AC is having a -2 dexterity bonus and subtracting your armor's magic plus from your AC. If you understand what the numbers are accomplishing, it's not a big deal, because you're never going to mistakenly add the +1 bonus of your plate mail to your AC, because obviously AC 3 is worse than AC 2, but it's still inelegant, and it's certainly less intuitive for newbies to grasp. But D&D had the whole attack table going on (and ACs based on naval warships, where 1st class is better than 2nd class), and THAC0 is just a work around for that.

                All other things being equal, I'd definitely push ascending AC over THAC0. And it's easy enough to convert descending AC and THAC0 to ascending AC and attack bonus, but maybe you're going for a nostalgia vibe, or maybe you'd like to use old modules without having to convert anything (sure each stat you convert is easy, but it's still something you have to do).

              • 1 month ago
                Anonymous

                Personally, I prefer a third option: roll under, though it tends to work better with systems where the numbers are somewhat... contained. And since I use armor as damage reduction rather than an accuracy-reducing apparatus, it's ideal.

                Anyway, with a roll under system, you have a target number based on your class and level (a sort of inverted THAC0). Maybe it starts of at 8. Any bonuses from strength or a magic weapon are added to that base number to give you an adjusted one (think base attack bonus plus whatever other bonus you have). You can write down that adjusted number, so you don't have to do even simple math on the fly. Roll it or under and you hit. Except you have to take your target into account. So you subtract their dexterity bonus, shield, magical pluses, and their armor, if you're taking a standard approach to AC. Everything goes in the right direction, with your pluses doing you good, and your enemy's pluses doing them good (no need for a -2 bonus to AC from dexterity). What is a little weird is that you're trying to roll low, as opposed to high, but that's consistent with old-school ability checks.

                The standard way of doing ascending AC and attack bonus is better in this last respect, because high is always better, including on your roll, but that's a relatively minor point in my book.

              • 1 month ago
                Anonymous

                I also prefer roll under mechanics but most players like big number = better.

  21. 1 month ago
    Anonymous

    OSRIC is only a reference, it does not attempt to explain the rules. Use the source material, the AD&D DMG, to address any confusion. Pic related

  22. 1 month ago
    Anonymous

    >how do I know the THAC0 of a class (Outside of calculating it, I couldn't find it in the book)?
    THAC0 is not the main calculation in 1e, it is a shorthand only mentioned in the back of the DMG, In 1e, it is assumed that you are using the values in the combat table.

    THAC0 is the primary (and only) combat resolution method in AD&D 2e, and the 2e PHB provides calculated THAC0 values for all classes in a handy chart

  23. 1 month ago
    Anonymous

    Just use Target 20. d20 roll + your bonus + enemy ac and you need 20 or higher to hit. Easy peasy,

    • 1 month ago
      Anonymous

      Addressing the different ways of using THAC0, the following needs to be true in order for you to hit...

      Die roll ≥ THAC0 - target AC

      And you can do the usual algebra thing of moving this from one side of the equation to the other. So take that equation and add AC to both sides and you end up with...

      Die Roll + Target AC ≥ THAC0

      Now subtract Die Roll from both sides of that equation...

      Target AC ≥ THAC0 - Die Roll

      Or to reverse the way it's being presented (since that's probably an easier way of thinking about it)...

      THAC0 - Die Roll ≤ Target AC

      As for Target 20, mentioned here
      (something I've never used), I guess it calculates THAC0 out of the equation. The base bonus it speaks of there is 20 - THAC0. Essentially, it's "how many points is your THAC0 better/lower than 20?" So 20 - THAC0 17 = 3 bonus. So now we replace THAC0 in our original equation (THAC0 = 20 - Bonus*).

      Die Roll ≥ THAC0 - Target AC
      Die Roll ≥ 20 - Bonus - Target AC

      Now add Bonus and Target AC to both sides of the equation, so we can get this in a more useful format...

      Die roll + Bonus + Target AC ≥ 20

      *If 20 - THAC0 = Bonus, Add THAC0 and subtract Bonus to both sides of the equation to get it to what you need to convert from THAC0: 20 - Bonus = THAC0.

  24. 1 month ago
    Anonymous

    The point of THAC0 is that you do the math and checks before a dice roll, rather than after every roll.
    People call it clunky but gameplay with THAC0 is faster than gameplay with positive AC. Harder to grok, better for play.

    As for knowing what THAC0 to use, you just look at the chart mate.

  25. 1 month ago
    Anonymous

    To reiterate what I'm sure other folks have already said, when D&D originally just used attack tables, like the one you posted in your picture. There, you just cross reference your class level and your target's Armor Class to get the number you need to roll (or higher) to hit.

    But that's a lot of space and information, and THAC0 developed as a way to quickly notate things. From it, you can calculate the number you need to hit any target. The stat appeared in all but name in the listing of monsters in the back of the Dungeon Master's Guide. It's an acronym for To-Hit Armor Class 0, and so it's literally just your target number vs. a target who has a 0 AC. So you can get it off any attack table by just looking at the AC 0 column (the red box in the pic I posted).

    If you look at the table, you'll note how it's 1 point easier to hit each successively higher AC. So a level 4 fighter needs a 17 or higher to hit AC 0 (giving him THAC0 17), but only a 16 or higher to hit AC 1, 15 up for AC 2, 14 up for AC 3 and so forth. So there's a pretty clear mathematical formula here. Your target vs. AC 1 is 1 point lower/better, AC 2 is 2 points lower/better, and so on. So just subtract the target's AC from your THAC0 to get your target number (THAC0 17 - AC 2 = target of 15). That's really all there is to it.

    You can also turn this equation around in the standard alegraic way, so that your THAC0 - your roll = the AC or worse (higher) you hit. So if your THAC0 is 17 and you an 11, you'd hit an AC of 6 or worse/higher (17 - 11 = 6). This is handy if the DM wants to keep your enemy's AC under wraps for a bit.

  26. 1 month ago
    Anonymous

    This ain't hard, people. You take your d20 and roll it. That number minus your THAC0, which is written on your character sheet, is the AC you are able to hit. You'd tell your DM what you can hit. That's it. If doing a bit of subtraction is beyond your mental capacity, you can write down a list of rolls and what AC they hit all in a neat little row on your character sheet.

    • 1 month ago
      Anonymous

      >This ain't hard, people. You take your d20 and roll it. That number minus your THAC0, which is written on your character sheet, is the AC you are able to hit.
      The irony...

    • 1 month ago
      Anonymous

      How did you get this so wrong when it was clearly explained just a few posts above.

  27. 1 month ago
    Anonymous

    Hey gang, is there an advantage to THAC0/descending AC over modern ascending AC? Im a moderngay and everytime I see descending AC, it just seems counterintuitive to me. Its not that I dont understand it, i just think its a roundabout way of getting the same result ascending AC gives you directly, i.e., figuring out the target number your attack roll needs to meet or exceed in order to land a hit. With THAC0, you need to consult these charts to figure out your target number. With ascending AC, the target's AC *is* the target number; no charts required. Is there something im missing with THAC0/descending AC? If people simply prefer it, thats fine and totally legitimate. What im wondering is if its doing something special that ascending AC isnt, if there's something im missing out on.

    • 1 month ago
      Anonymous

      >i just think its a roundabout way of getting the same result
      That's because it (barely) is.
      The difference is negligible.

      Roll over AC, compared to THAC0, really just shuffles a single variable around (AC) so that instead of AC being attacker side in the math, it's target side instead.

      In THAC0:

      Addressing the different ways of using THAC0, the following needs to be true in order for you to hit...

      Die roll ≥ THAC0 - target AC

      And you can do the usual algebra thing of moving this from one side of the equation to the other. So take that equation and add AC to both sides and you end up with...

      Die Roll + Target AC ≥ THAC0

      Now subtract Die Roll from both sides of that equation...

      Target AC ≥ THAC0 - Die Roll

      Or to reverse the way it's being presented (since that's probably an easier way of thinking about it)...

      THAC0 - Die Roll ≤ Target AC

      As for Target 20, mentioned here
      (something I've never used), I guess it calculates THAC0 out of the equation. The base bonus it speaks of there is 20 - THAC0. Essentially, it's "how many points is your THAC0 better/lower than 20?" So 20 - THAC0 17 = 3 bonus. So now we replace THAC0 in our original equation (THAC0 = 20 - Bonus*).

      Die Roll ≥ THAC0 - Target AC
      Die Roll ≥ 20 - Bonus - Target AC

      Now add Bonus and Target AC to both sides of the equation, so we can get this in a more useful format...

      Die roll + Bonus + Target AC ≥ 20

      *If 20 - THAC0 = Bonus, Add THAC0 and subtract Bonus to both sides of the equation to get it to what you need to convert from THAC0: 20 - Bonus = THAC0.

      So
      >Roll + modifiers (including target AC) >=20 is a hit
      (Except it would also include a very dumb -20 modifier on both sides to make the target 0 instead of 20, because the system is centered on AC 0, so more like
      "Roll + modifiers + target AC (- 20) >= 20 (- 20)", but that's stupid and pointless and I digress)

      In a target AC system:
      Roll + modifiers (which no longer includes enemy AC) > 0 (or in THAC0, this would be "20 (- 20)") + enemy AC (it moved over here instead) is a hit.
      And since + 0 doesn't matter, you can remove it, leaving only:
      >Roll + modifiers >= enemy AC is a hit

      Which means that all it actually does is remove a single step from the equation, the one where you would compare the end result to a fixed value (20 or 0), and instead you move one of the variables (AC) to take it's place.

      Once you look at it, is the math basically the same and you'd have to be a moron not to be able to do one if you can do the other?
      That's a yes.
      Is the final step actually superflous when compared to the more streamlined math of a roll over AC system?
      That's a yes.
      Does any of that even matter?
      You better believe that's a yes.
      All of Ganker always goes "stop liking what I don't like", and edition wars is just the local /tg/ flavor of it so /tg/ wouldn't exist without pointless arguments on THAC0.

    • 1 month ago
      Anonymous

      >Hey gang, is there an advantage to THAC0/descending AC over modern ascending AC?
      No, it's just how it evolved in older editions. If you're playing an older edition or clone, use it, it's baked-in to the rest of the combat stats. If you're playing a different game, use whatever it uses. No useful purpose is served either by converting THAC0 to ascending, or ascending to THAC0 - it simply isn't worth the effort.

  28. 1 month ago
    Anonymous

    It’s the number you need to roll to hit Armor Class 0. If the enemy’s AC is higher, you subtract from your roll (making it easier).
    I mean, it’s pretty simple. Base attack bonus is better but THAC0 is more grounded by being pinned to a specific number.

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