e75773c93af04a34b10c94327f83fd32
AMR says 668 defense rating is 5.44%, yet in-game, 668 defense rating is only 5.40%.
The difference is just rounding… the character sheet in-game truncates when showing defense skill whereas we do typical rounding.
I honestly don’t know if that is just how they display it, or if the game actually does truncate when calculating the chances – it changed from expansion to expansion and it is one of those things that is so small that it is not well-documented or tested (as far as I’m aware).
I would hope that under the hood is rounds instead of using the truncated value in WotLK, but if you have a source that has proven otherwise, let me know. Unfortunately the game’s character sheet is not a reliable source for these cases.