THAC0 is an acronym for "To Hit Armor Class 0" and it is discussed
on page 76 of the manual. However, that discussion is a little sparse,
so I will embellish it with some information from AD&D 3rd addition
rules.
Lower THAC0 is better! THAC0 is the MINIMUM roll you need
to be able to hit an enemy with an armor class (AC) of 0 ( yes, lower
armor class is also better as discussed above ). You must score a
hit before you can do any damage!
When you attack an enemy, you SUBTRACT his AC from your THAC0 and the
result is the minimum number you have to roll (on a 20-sided die)
to be able to score a hit. To-Hit is always rolled on a 1d20
die (resulting in a number from 1 to 20). The BG manual states that
a natural 1d20 roll of 20 ALWAYS hits (and will cause a critical
hit), and a natural roll of 1 ALWAYS misses (where "natural" roll means
an unmodified 1d20 roll). The BG manual also states that critical
hits cause double damage!
Some examples:
-
Enemy AC = 0, your THAC0 = 8 (including any to-hit adjustments) ,
your 1d20 roll must be equal to or greater than 8, (8 - 0 = 8),
to be able to score a hit on the enemy. So you have 13/20 (13 out
of 20) chances to hit.
-
Enemy AC = -2, your THAC0 = 8 (including any to-hit adjustments) , your
1d20 roll must be equal to or great than 10, (8 - (-2)) = 8 + 2
= 10, in order to score a hit. So you have 11/20 chances to hit.
-
Enemy AC = 5, your THAC0 = 8 (including any to-hit adjustments) , your
1d20 roll must be equal to or greater than 3, (8 - 5 = 3),
to be able to score a hit. So you have 18/20 chances to hit.
-
Enemy AC = 8, your THAC0 = 5 (including any to-hit adjustments) ,
your 1d20 roll must be equal to or greater than -3, (5 - 8 = -3).
But how can you roll "-3"? Well, you cannot since the lowest
value you can roll on a 1d20 die is "1"! So although the -3 result
should indicate that you should score a "sure hit", there is still the
rule that states that a roll of 1 is ALWAYS a miss, so your chance of hitting
your enemy is actually 19/20 (19 chances out of 20), or you must get a
2 or higher on your 1d20 roll in order to hit your enemy.
The game displays your Adjusted THAC0. Each character class has a
base THAC0 (see below) which changes with his experience level. This
base THAC0 is adjusted by any THAC0 modifiers. For example, a level
3 warrior (with a base THAC0 of 18) is wielding a weapon with a +2 "to-attack"
modifier, therefore his adjusted THAC0 would be 16 (18 - 2 = 16), and it
is this adjusted THAC0 that would be used in calculating whether he was
able to hit the enemy.
Generally, lowering your THAC0 by 1 will increase your
chance by 1/20 of of hitting your enemy.
Your THAC0 changes based upon your character's class, type weapon wielding,
type ammunition used in weapon (some arrows/missiles as well as slings
and bows have +'s to attack), character's level (your THAC0 will decrease
as you go up levels an amount depending upon character's class), weapon
specialization skills, etc.
-
THAC0 modifiers due to weapon specialization: The table on
page 93 of the manual shows the bonus "to-hit" for various levels of weapon
proficiency. For example, a proficiency of "Specialized" results
in a bonus to-hit of +1 whereas a proficiency of "Proficient" has
no bonus to-hit.
-
THAC0 modifiers due to magical weapons and items: Some weapons
are enhanced and have a bonus to-hit modifier. For an example, a
1d8 +2 weapon will lower your THAC0 by 2. There are also some magical
items that can modify your THAC0. For example, the Gauntlets of Weapon
Expertise (see our Special Items page) have a +1 THAC0 bonus (will lower
your THAC0 by 1).
-
THAC0 modifiers due to strength: Table 1 on page 134 of the
manual shows to-hit adjustments due to the strength of the character.
For example, a character with strength 3 would have a -3 to-hit adjustment,
i.e., his THAC0 would be increased by 3. A character with strength
18 would have a +1 to-hit adjustment, i.e., his THAC0 would be reduced
by 1.
-
THAC0 modifiers due to Dexterity: . Table 1 on page 134 of
the manual shows the missile weapon to-hit adjustment for dexterity.
For example, a character with 3 dexterity would have -3 to-hit (missile)
adjustment, i.e., his THAC0 (for missile attacks) would be increased
by 3. A character with 18 dexterity would have a +2 to-hit
(missile), i.e. his THAC0 (for missile attacks) would be reduced by 2.
-
THAC0 modifiers due to class/level: AD&D rules indicate
the following THAC0 modifiers based on character Class and Level.
Class vs. Level |
|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
Priest |
20 |
20 |
20 |
18 |
18 |
18 |
16 |
16 |
16 |
Rogue |
20 |
20 |
19 |
19 |
18 |
18 |
17 |
17 |
16 |
Warrior |
20 |
19 |
18 |
17 |
16 |
15 |
14 |
13 |
12 |
Wizard |
20 |
20 |
20 |
19 |
19 |
19 |
18 |
18 |
18 |
|
-
Other: There are also spells and potions that can improve
THAC0.
|