Question about Defense

I'm new to theory-crafting, so please bear with me.

At level 80, my defense is at 496. When I mouse over it, it reads "Defense 496 (400+96)". I'm assumed that the +96 was coming from my gear, but when I added it all up, my gear has a total of +453 defense rating. What am I missing?

Thank you, and please forgive my noobish-ness.

Defense Skill <> Defense Rating

Divide your Defense Rating by ~4.9 iirc to get the Defense Skill your gear is giving you.
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Levantine: 80 Frost [27k HP, 27k Armor, 544 Def]
Anzen: 30 Elemental [Resto in the making]

Can't hurt to add: You need a total of 689 Defense rating to get the 540 minimum.
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4.918 defense rating = 1 defense skill

See "Rating Conversions" at http://maintankadin.failsafedesign.com/viewtopic.php?p=263221#263221

689 / 4.918 = 140.0976 when added to your 400 base defense skill, this gives you 540.
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Gyrnax -- Tankadin