There are many different resistances. The main four are Ranged, Melee, Magic and Physical. Note that Melee and Ranged resistances are also considered Physical damage, and thus are effective against Rouges and Warriors. Magic Resistance is primarily used to negate damage from Mages. Not that the bonuses from Cm's aren't show on the stats on the loading screen or in the battle. They are included in damage calculations but aren't easily known.
See here for a special resist designed for ai.
How resistance work were recently changed, This is the order they take effect
AI Defense ->
Armor -> Resist Damage Reduction -> Global Reduction ->
Elemental Resistance: There is one variety for each of the elemental types of damage. While the main resistances are effective in a general sense, elemental resistances are applied for more niche uses. For example, Arcane resistance is very useful in brawls Mages use their basic Arcane Shot. The different resistances include Arcane, Fire, Lightning, Ice and Nether.
Stun Resistance: Helps you not get stun locked, although speed can also add to recovery from stun. Other resists can lessen the effects of stun. This is particularly useful against glass cannon builds who primarily use stun.
Other types of effect resistances include poison, burn, and bleed resist. Although not widely used, they can be useful against effect builds who depend on stacking these effects to win. A warrior can use the skill: Bandage Wounds to get 50% resistances in these three effects, so it is not recommended to invest in these resistances for warriors. Due to recent updates if you are a full tank build its worth to get these resistance on Combat masteries to add to you global resist bonus.
Armor: Now is included in the global resist calculation. With armor/10 added to the global resist formula.
It's important to note how stacking resist will effect the overall damage. Without getting too complicated on the damages with elemental bonuses on physical attacks being reduced with magic resists. Will keep the main source of the damage. Also ignored armor.
First note that 50% melee/ranged res and 50% physical res aren't added together but are multiplied. So the resuilt of the total damage negated is different.
can use this calc which has a damage calc and includes armor and piercing.
The primary resist below are the class based ones.
LevelMod =1+(Primary Resist) * 0.05
reduction = LevelMod / (LevelMod^1.7)
Damage = Damage * reduction (if reduction % is greater than resist value then damage blocked will = resist value)
|Resist value||Damage blocked %|
Global resist Edit
This is a bonus resist added on from the rest of your resists.
(all Resist total+(armor/10))/20
Calculation order Edit
In example use 1000 ranged damage, with 25% physical resist, 25% ranged resist and 10% with global resist.
1000*0.75*0.75*0.9 = 506.25 (round) 506