Armor Value or AV is the amount of damage a suit or natural armor absorbs from a successful attack. Armor and all magic plusses on it, in addition to all magic that simulates armor does not improve AC, but bestows an AV instead. A hard and fast way to figure out the amount of AC to apply to each area is by considering both the size, and the speed of the creature. Smaller creatures get some AC from their small size. Thus, his full AV is 13, with 4 extra points of toughness.
Dragons suddenly become very tough.
Most attacks just bounce off its hide and bulk, making these beasts very dangerous for all but the most powerful heroes. There is 1 other I will discuss later, but it is a special attack form. Base AV applies in full against Slashing attacks and against most Piercing attacks as well. AV against Blunt attacks acts in a special way. Toughness is not halved in this way, but applies in full.