ok, here is how item values are calculated, Cob may need to update us if anything has changed:
This system took a long time to develop and a long time for Cob to code. So hats off to him and the tappers/officers/members that contributed.
DKPCost = [(ItemLevel*2+(ItemLevel*SlotValue))/3 * (ColorValue)]
ITEM SLOT MULTIPLIER
0.0 Shirt, Projectile, Bag, Tabard
0.6 Cloack, Neck, Finger, Tricket
0.65 Feet, Hands, Shoulders, Waist
0.9 Head and Legs
0.95 Chest/Robe
0.95 One-hand, Off-hand, Ranged Weapons, Held in Off-hand, Idol, Shield
1.7 2-Hand Weapons
ITEM COLOR MULTIPLIER
0.90 Blue
1.0 Purple
1.05 Orange
Now, about the values. ItemLevel is actual level of the item that blizzard has assigned it. This is a very good indicator of comparison between two objects. It's not available in-game, but it is inside the ItemCache.wdb files; and you can see the exact value of each item over on goblinworkshop if you like. Thottbot et all also displays it on their tooltips I believe.
ItemSlotMultiplier -- this is more arbitrary, but based on a wow wiki study of how blizzard assigns stats to various slotted items. These numbers aren't the best idea for comparisons I think. Weapons generally have less stats than armor, but are pretty desirable for other reasons.
ItemColorMultiplier -- I know you're thinking 'purples have so much better stats than blues, why would a blue only have a 5% markdown?' Well, the answer here ties back to item level. For example, when you kill Onyxia you get a ItemLevel 76 Bloodfang Hood. The same monster drops an ItemLevel 60 Stonegrip Gauntlets which has much lower stats. The truth is, if Onyxia dropped level 76 blue items, they would be only slightly inferior in stats/etc to the Bloodfang Hood.
