AC

Armor Class AC is a rating of how much armor your character is wearing.
This number ranges from 100 to -100, with 100 being the worst and -100 being
the best. The lower your AC the harder it is for others to hit you with
a hand-to-hand attack. What this means is that AC has no bearing on spell
casting. While it is possible to get your AC lower than -100, this has
no bearing on the game in any way.

The armor class scale is:

  100 Naked person
    0 Heavily armored
 -100 Divine armor

Equipment can affect your AC in two ways: an Armor affect or an AC-apply
affect. The number in the Armor affect is a direct change to your AC Any
piece of equipment can affect your AC in this way. The number in the
AC-apply affect, which appears only on equipment of type ARMOR reduces
your AC more if the equipment is worn on the body than if it is worn
elsewhere.

Example object identification:

AC-apply of 5
Affects:
    -10 to ARMOR

This piece of armor will reduce your AC by 10 no matter where it is worn;
it also has an AC-apply of 5, which will reduce your AC by a multiple of 5
depending on which equipment slot it takes up. Note that for the ARMOR
affect, negative is good (reduces your AC For AC-apply, positive is good.