A while back Duck posted some information in a WE buffs thread that recently I realised is vitally important to new players and to old players who may need to look up mechanics. I had to trawl through the history in discussions to find the post in response to a question from a fellow TW Warhammer player. So @CA_Duck
Is it alright if we have this pinned on the forums? Or could even a moderator pin this? I just copy and pasted your post Duck I hope that was alright. This information is so useful.
Armour = Max damage reduction percentage. Min is always 50% of armour value. To be more precise, any time base damage is dealt, the target rolls for armour. This armour roll is a random value between 50% and 100% of the armour stat. The armour roll is then applied as percentage damage reduction. E.g. a unit of Swordsmen with 30 armour can roll between 15 and 30 percentage damage reduction.
Attack and Defense are additive modifiers to hit chance. So +1 attack means +1% hit chance, while +1 defense means -1% chance to be hit. Base hit chance is 40%, min is 10% and max is 90%, so having more than +30 defense than the enemy's current attack is ineffective. Respectively having more than +50 attack compared to enemy defense is ineffective. Defense can be reduced by 40% from attacking an entity from the side and by 75% when attacking the rear of an entity.
Charge bonus adds additively to attack and damage if a unit has charged into combat. It is at max on the first second of engagement and is linearly reduced over 15 seconds. The damage increases uses the existing ratio of ap-to-base damage to determine how much of each it should add. E.g. a unit with 12 charge bonus and 25% ap damage, will get +12 attack, +3 ap damage, +9 base damage on the first second of the engagement.
Bonus vs. large/infantry adds additively to attack and damage like charge bonus, but only against a certain entity size. It's a constant bonus. It's damage increase uses the same ap-base ratio system as charge bonus.