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Article 1:
THAC0 and Armor Class (
AC)
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THAC0 = "To Hit Armor Class 0", of a 20 sided dice the number needed to hit
an enemy with an
AC of 0. For example, if the
THAC0 is 19, a roll of
19 or higher is needed to hit an enemy with an
AC of 0. A roll of
1 is always a miss, and a roll of 20 is always a hit, called
CRITICAL MISS and CRITICAL HIT respectively.
AC = Armor Class, roughly how difficult a figure is to hit.
AC starts
with a base score of 10 and is improved by lowering the number.
Therefore a 0
AC is better than a 10, and a -10 is better still.
These two things are what determines when a hit (that scores damage) is made.
THAC0 is the offensive end of the roll, and
AC is the defensive end of the
roll.
A successful hit is decided when the random roll is greater than the
attacker's
THAC0 - enemy
AC. If a 15
THAC0 Fighter attacks a 0
AC goblin then you must roll 15 or greater. (The game itself usually does the
rolling for you, but it still follows these mechanics) Remember that a roll
of 20 will always hit. So, even if the goblin's
AC was -400, if you roll a
20 you will still hit it. If the goblin has 10
AC then you need only roll a
5 or better, etc. (
THAC0 - EnemyAC = 15 - 10 = 5)
Note: Just because you hit, that doesn't mean you'll deal damage. There is
the concept in second edition
D&D of weapon immunities. Some monsters
require a certain type of weapon to be hit. Also, wizards can cast
spells such as "Protection from Magic Weapons" which makes them
temporarily immune to magic weapons. Baldur's Gate represents this by
having characters say "my weapon is useless" or something similar.
THAC0 Explained:
----------------
THAC0 defaults at 20 and is gradually lowered when levels are gained.
Depending on the class (i.e. Fighter, Cleric, Mage) of the person involved
the
THAC0 will decrease at different rates. For a Fighter (or Ranger, or
Paladin)
THAC0 decreases by a score of 1 per level. A level 1 Fighter
starts at 20
THAC0, but by level 10 he is at 11. (He has gained 9 levels,
and so loses 9
THAC0) The lower the
THAC0 the better, and there is no
limit to how low it can go.
THAC0 Progression by Level & Class Chart:
Level
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
----- --------------------------------------------------------------
Warrior 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5
Wizard 20 20 20 19 19 19 18 18 18 17 17 17 16 16 16 15
Priest 20 20 20 18 18 18 16 16 16 14 14 14 12 12 12 10
Rogue 20 20 19 19 18 18 17 17 16 16 15 15 14 14 13 13
Patterns
--------
Warrior 1 every level
Wizard 1 every 3 levels
Priest 2 every 3 levels
Rogue 1 every 2 levels
At this point we're still just referring to RAW
THAC0, there are still
several things that modify it before it is used. There are, in fact, four
main things that modify
THAC0 from here: Strength, Weapon, Special
Effects, and Proficiency. A super low strength score will raise your
THAC0 (which is bad), while super high Strengths will lower your
THAC0 (which is
good).
STRENGTH as a
THAC0 modifier
STR
THAC0 Adj. STR
THAC0 Adj.
3 -3 17 +1
4 -2 18 +1
5 -2 18/01-50 +1
6 -1 18/51-75 +2
7 -1 18/76-90 +2
8 0 18/91-99 +2
9 0 18/00 +3
10 0 19 +3
11 0 20 +3
12 0 21 +4
13 0 22 +4
14 0 23 +5
15 0 24 +6
16 0 25 +7
Notice how any improvement in
THAC0 is denoted by a +3 or a +4, while in
fact these numbers are how much your
THAC0 is DECREASED. A level 1 Fighter
has 20
THAC0, but if he has 18/00 STR, his
THAC0 is decreased to 17.
The weapon used also has an effect on
THAC0, both by the weapon itself and
also through Proficiency (although Proficiency is an optional rule, and
of the games listed at the top, only Baldur's Gate, Planescape: Torment,
Icewind Dale, and Baldur's Gate II follow this rule). Generally speaking,
the amount the
THAC0 is changed is the number after the +. A Long Sword +1
would improve
THAC0 by 1 point. There are exceptions to this, some weapons
won't have a + but improve
THAC0 anyway, and some will say +1, but will in
fact improve
THAC0 more than 1 point. In these cases, checking that items
information will reveal how it modifies
THAC0 (only available in some
games).
Note: To check the item information in
BG1,
BG2 and
IWD, right click the
item in the inventory screen. Also note that magical items are very
often "NOT IDENTIFIED." Meaning that you won't know what they do
until they are IDENTIFIED. See the FAQ below.
Special Effects can be either a spell that improves
THAC0 (Bless, for
instance), or an Item that improves
THAC0, but isn't a weapon, such as an
Amulet of
Thac0 +1.
Proficiency was introduced to show what your character is skilled in, or
not skilled in. It has only really been used since Baldur's Gate in 1998.
Since proficiency represents your character's knowledge of the weapon being
used, using a weapon that you don't have proficiency in will result in a
penalty to
THAC0 and to Damage.
PROFICIENCY as a
THAC0 Modifier: (Baldur's Gate I & II, Icewind Dale,
Planescape: Torment only)
Level of Proficiency Points Spent Bonus to Hit
Non-Proficient 0 -2 (Warrior)
-5 (Wizard)
-3 (Priest or Rogue)
Proficient 1 0 (but there is no penalty)
Specialized 2 +1
Master 3 +3
High Master 4 +3
Grand Master 5 +3
As you can see, a Wizard using a weapon that he isn't proficient in will
result in a steep penalty, so he could have 20
THAC0, but because he is
using the wrong weapon his
THAC0 leaps up to 25.
Dexterity Note: Dexterity has one small effect on
THAC0, but only towards
the use of MISSILE WEAPONS (bows, crossbows, etc.). At
a DEX of 16 you get a +1 to hit, 17 & 18 +2, and 19 +3.
Armor Class Explained:
----------------------
Armor Class isn't really about armor. It is the composite of Armor and
Dexterity that determines how hard it is for a damaging hit to be made.
The base Armor Class (
AC) is 10. Anything lower is better and makes your
character harder to hit. It does NOT reduce the amount of damage taken.
The first facet of Armor Class is your Dexterity Score. The higher the
Dexterity, the lower (better) your Armor Class. This reflects your
character's ability to dodge attacks. So, here, negative numbers are
better.
DEXTERITY as an Armor Class Modifier
DEX
AC Adj. DEX
AC Adj.
3 +4 14 0
4 +3 15 -1
5 +2 16 -2
6 +1 17 -3
7 0 18 -4
8 0 19 -4
9 0 20 -4
10 0 21 -5
11 0 22 -5
12 0 23 -5
13 0 24 -6
25 -6
Whether you are on level 1 or level 20 your
AC is still determined by the
same two factors, DEX and Armor. So, a level 1 Fighter with a Dex of 18
would have an
AC of 6 (before putting any armor on, BASE
AC(10) +
DEX ADJ.(-4) =
AC). A level 20 fighter who has no armor would have the
same
AC with the same DEX.
Which brings us to the BULK of where
AC is made up, Armor. We will divide
armor into two categories, actual Armor (such as Plate Mail Armor) and
support Items (such as Ring of Protection +1).
Armor usually lists what your
AC will be based from the Base
AC itself.
So Leather Armor will list its
AC as
AC 8. What this means is that if you
had the base
AC of 10, wearing Leather Armor will decrease your
AC to 8.
If you do NOT have the Base
AC (and who does), it still decreases your
AC by 2 points. If we wanted to determine the
AC of our 18 DEX Fighter
wearing Leather Armor we would need to take the Leather Armor
AC(
+
Dexterity Bonus(-4) to get 4. In this way you can think of your Armor's
AC as REPLACING your Base
AC. So instead of starting at 10, with Leather
Armor you would start at 8.
Armor as an
AC modifier (not all armors are in all games)
Armor
AC Leather Armor 8
Studded Leather 7
Hide Armor 6
Scale Mail 6
Brigandine Armor 6
Chain Mail 5
Ring Mail 5
Elven Chainmail 5
Drow Chainmail 4
Banded/Splint Mail 4
Plate Mail 3
Field Plate 2
Full Plate 1
If an armor is said to be +1, or +2 that means that the armor has an extra
special bonus attached that further lowers
AC by that number. So a Chain
Mail +4 would have an
AC score of 1 rather than 5.
In addition to your Armor,
AC is also determined by special items being
worn by the character. The most common special item is the common shield
which improves
AC by one point (our 4
AC, 18 DEX Leather Armor Fighter
would then drop to 3
AC with a Shield). There are various varieties of
shields, but they all do the same job. Other items would be Rings of
Protection or Cloaks of Protection. These all improve the
AC of the
wearer.
Note: Some games (Baldur's Gate, for example) allow only ONE extra
protective item (not counting shields) to be worn at a time. This
includes Magic Armors. So, if you wore a Chainmail +1, you
couldn't wear a Ring of Protection +1. Or, if you had that
Ring of Protection +1 you couldn't wear the Cloak of
Protection +1.
Magic can also function as armor, however, it usually acts in place of
armor rather than as a bonus to it. Take the spell "Armor" or "Shield" for
example. They set your
AC to 6 and 4, respectively, but if you're wearing
armor better than either, you get no extra benefit. There are some spells
that provide a simple bonus, such as Defensive Harmony (
BG1,
BG2,
IWD), so
check spell descriptions.
