Determine Other Numbers and Rolls
Armor class, attack rolls, and saving throws are numbers which you'll calculate from the character's other attributes or find on provided tables which are important to the way the character performs in combat.Record your armor class, sometimes abbreviated as AC, is a number indicating how tough it is to hit your character. With the
armor class, unlike most numbers in the D&D game, a low number is good for a character, and a high number is bad. Your armor class is a combination of the type of armor you are wearing, plus any adjustments due to Dexterity. First, find your armor type on the Armor Type and Armor Class Table.Once you know your armor class as provided by your armor type, you can determine adjustments to your armor class from your Dexterity. Find your Dexterity score on the Bonuses and Penalties For Ability Scores table. For every +1 on the table, subtract 1 from your armor class. For every —1, add 1 to your armor class.
Record your THACO: The abbreviation THACO stands for "To Hit Armor Class 0." There's nothing mysterious about it: It's just the number your character needs to roll to hit an armor class of 0. To use THACO, you have to do some adding and subtracting during combat. You subtract your modified attack roll (the number rolled on a 20-sided die plus any bonuses) from your THACO, and the result is the armor class your character hits. When in combat, this should be copied from the dice roller page and pasted into an Out of Character line of your post for the active GM scene.
For example, Ruggin is a 3rd level dwarf, and he's fighting a hobgoblin clad in chain mail (AC5). Ruggin's THACO is 19, and he rolls a 16; Ruggin successfully hits his opponent's armor class (19-16=3) since he hit an AC3 (two better than AC5).
Record Adjustments for Ability Scores. You've already seen, on several occasions, that high abilities give your character special bonuses, while low ones give the character special penalties. Below are the character's abilities and notes on what sorts of adjustments high and low abilities will bring him.