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What does To-Hit roll calculate?

So in 2e AD&D Thac0 is a difficulty check (DC).
The way it works is simple: You roll a d20 and add the enemy's armour class to the roll. If the result meets or exceeds your character's Thac0, you score a hit.
Alternatively, you subtract your roll from your Thac0 and if you score lower that the armour class, you hit.

In Icewind Dale however, this does not seem to be the case.
The to-hit roll looks something like this: e.g 11 + 2 = 13 (Miss)
The first number is obviously the d20 being rolled. The second number does not appear to be enemy armour class as explained above, instead it appears to be calculated by adding or subtracting armour class from Thac0, or vice versa. The second number will be different, depending on who is attacking.

I have no idea what the result is supposed to be, only that a high result is the goal.
Since Thac0 appears to already be included in the calculation it is clearly not trying to meet or exceed Thac0. This is especially evident when you compare it to character Thac0. My Monk has a Thac0 of 9 and a base Thac0 of 11, yet scoring a 12 in the To-Hit calculation still results in a miss.

So my question is, What is the result calculating? How am I supposed to read the To-Hit rolls so that they may provide meaningful feedback?

Comments

  • jmerryjmerry Member Posts: 2,644
    The first number is the base d20 roll. The second number is a compilation of bonuses such as strength/dexterity, weapon enchantment, specialization, spell effects, and AC modifiers versus damage types.
    Your base THAC0, and the enemy's AC, are invisible in this. If the final number is at least (your base THAC0) minus (the enemy's AC), you hit. If not, you don't.

    Some effects can boost your base THAC0, though it's a lot rarer than showing up in the bonus number. Dexterity AC bonuses are included in the AC, rather than cutting into the attack bonus.
  • VWoodVWood Member Posts: 11
    jmerry wrote: »
    The first number is the base d20 roll. The second number is a compilation of bonuses such as strength/dexterity, weapon enchantment, specialization, spell effects, and AC modifiers versus damage types.
    Your base THAC0, and the enemy's AC, are invisible in this. If the final number is at least (your base THAC0) minus (the enemy's AC), you hit. If not, you don't.

    Some effects can boost your base THAC0, though it's a lot rarer than showing up in the bonus number. Dexterity AC bonuses are included in the AC, rather than cutting into the attack bonus.

    Thank you for the reply.

    O.k. So, if I understand you correctly, you're saying that the second number is calculated only on modifiers? i.e. attacker's To-Hit modifiers, such as Strength bonus, enchantment etc., as well as the the target's modifiers to AC, such as armour enchantment and Dexterity bonus.
    Meanwhile the result that the attack calculation is trying to achieve is itself based on another calculation, which is current total attacker Thac0 modified by current total target AC?
    That seems like such a bizarrely odd way of calculating it.
    It would make a lot more sense if the second number was simply the target's current AC after all modifiers, and the result required was the attacker's current Thac0 after modifiers. That would make complete sense and give accurate feedback. We would know what the target's AC is to beat and the result required to hit (our Thac0).

    So then, with the way it is now, there is no way to know what the calculation should be to hit, except for watching the rolls, for a specific character, during each specific fight, and then trying to determine what the roll needed might be. I suppose that makes it kind of like tabletop where the DM keeps the enemy AC secret and you just have to get a feel for what you need to roll.
    I have been playing this game for 20 years and I have never been able to make heads or tails out of the To-Hit roll any more than that. I would love to see the game's calculation under the hood.

    I appreciate the response.
  • jmerryjmerry Member Posts: 2,644
    The AC modifiers that show up on the "to hit" side are the specific type modifiers, like plate mail's bonus against slashing attacks. Stuff like dexterity bonuses to AC, shield bonuses, and the +N on enchanted armor (which doesn't mean anything intrinsically) go into the invisible armor calculation.
  • Jim_Infinite_1965Jim_Infinite_1965 Member Posts: 1
    edited March 21
    Hello, my friends. If you don't mind I want to get a little help from you.
    I'm playing Icewind Dale: Enhanced Edition right now and I don't understand how THACO info numbers work in my gameplay messages. (I turned Feedback - To Hit Rolls in Options)

    For example:

    Fighter vs Paladin:

    Fighter THACO: 20 (20), Armor Class: 8 attacks with Quarter Staff 1D6
    Paladin THACO: 20 (21), Armor Class: 8

    Fighter - Attack Roll 2 + 0 = 2 : Miss,
    Fighter - Attack Roll 12 + 0 = 12 : Hit the Paladin - Damage Taken (4).

    Paladin vs Fighter:

    Paladin with Quarter Staff 1D6 attacks Fighter

    Paladin - Attack Roll 8 - 1 = 7 : Miss
    Paladin - Attack Roll 16 - 1 = 15 : Hit the Fighter - Damage Taken (7).


    Could you explain what each of these numbers means?
    Thank you.
    Post edited by Jim_Infinite_1965 on
  • UnsanityUnsanity Member Posts: 48
    edited March 19
    Jim_Infinite_1965

    As I understand it, Thac0 = To Hit Armor Class 0. If your Thac0 is 20, you need a roll of 20 to hit Armor Class 0. Monsters have a Thac0 score as well. Depending on your Armor Class, the monster may need a high or low roll to hit you.

    If your fighter or paladin has an Armor Class of 8 and the monster has a Thac0 of 20, then the monster needs a roll of 12 or better to hit it you. It rolled a 12, so it you. Better equals less, if I am getting this right. So if that monster rolled a 13, it missed. If that monster rolled an 11, it hit. Now there are critical hits. If the monster rolled a 20, it not only hit you, but it hit you good. Double the damage. Now, if the monster can only hit you with a 20, then the critical hit rule doesn't apply because the monster wasn't wasn't good enough/a challenge if you will. I think that applies to this game, but I am not sure.

    That's as I understand it. I haven't played any tabletop D&D games, but I have played a lot of the computer games, and for a while they all followed the 2nd Edition rules. 3rd edition rules being completely different. The higher the roll the better. Easier math.

    Also, weapon proficiency takes a role. I don't know what the penalty for using a non-proficient weapon is, I would have to look that up in the manual. So, if both of your characters are using a Long Sword and only one of them is proficient in it, that character's Thac0 would be lower (better).

    Then you also have a Thac0 table based on your class. Fighters, Paladins, and Rangers have the same Thac0 table and the best one. Thac0 decreases by one point a level. If I remember looking at Thac0 charts, Mages have the absolute worst. That does make sense. Clerics don't seem to have that great of a Thac0. I can't remember if theirs is worse or better than the Rogues. Rogue being a Thief or a Bard. Of course you have all the IWD:EE classes too.

    I think I found a Thac0 chart here on this site. Either that or in the PDF manual that comes with the game.

    Also to add to this little equation is the Strength (melee) and Dexterity (range) attribute. If one character's strength is higher than the others, then that one gets a better Thac0 as well.

    Melee weapons is Class + Strength + Proficiency + Weapon + Race if applicable = Your Thac0 score.
    Range weapons is Class + Dexterity + Proficiency + Weapon + Race if applicable = Your Thac0 score.

    To add more to the equation, there are spells, potions, and magic abilities that can change your Thac0 for better or worse.

    Just focusing on the melee aspect, some examples.
    1/2 Orcs can have a Strength of 19. That helps with Thac0 and damage.
    Fighters excel in weapon mastery. More pips you put into a weapon, the better your Thac0 and damage will be.
    Elfs get a +1 to hit with Long Swords. Such a common weapon, a lot of magic ones.
    Ranger gets a bonus to hit and damage vs. a chosen enemy.
    Assassin (Thief Class Kit) gets a +1 to hit and Damage.

    One more thing. Using 2 weapons at a time also effects your Thac0. You can specialize in 2 weapon fighting to minimize the penalty to hit, Thac0. Fighters and Rangers once again come to mind with that, single or multi-class. Rangers being the better choice since you start with 2 or 3 pips in 2 weapon fighting.

    That should cover the basics? There are more proficient players out there that can explain it better than me, that and the game manual itself. It has all the tables and such. Speaking of, I forgot I had it on my favorites bar. I refer to that every time I have an idea for a character. Usually my idea doesn't work. Thus is life huh?

    https://cdn.icewinddale.com/files/IWDEE-Manual-2-Mastering-Melee-Magic.pdf

    Well, I hope that helps a little bit.
  • jmerryjmerry Member Posts: 2,644
    I'm assuming that your (@Jim_Infinite_1965) examples are level 1 characters without staff proficiency, wearing no armor. The fighter has strength somewhere in the 18/51 to 18/99 range. The paladin has strength somewhere in the 17 to 18/50 range. Both characters have 16 dexterity.

    So now, these characters both have base THAC0 20 and base AC 10. Both characters get a -2 bonus to AC from dexterity, for a final AC of 8. No type modifiers, because no armor to grant them.
    The fighter gets -2 to hit from non-proficiency and +2 to hit from strength, for a net modifier of zero. So you see that "+0" in the attack roll. The modified value they need in order to hit is (base THAC0) - (final AC) = 20 - 8 = 12, which they get on a natural 12 or better.
    The fighter gets -2 to hit from non-proficiency and +1 to hit from strength, for a net modifier of -1. So you see that "-1" in the attack roll. The modified value they need in order to hit is (base THAC0) - (final AC) = 20 - 8 = 12, which they get on a natural 13 or better.
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