This' a graph that is stolen from the protection thread from EJ.
http://img835.imageshack.us/img835/118/graph3t.jpg
How to use:
Check your total avoidance ratings with buffs on and place the numbers at the bottom of the graph.
Check how much mastery rating you've got with buffs, and place accordingly to the colors over the total avoidance, the numberes are written on the picture.
Then go to the left and see which Parry to Dodge ratio you should be having.
If you've got a total avoidance rating of 2200 and a mastery rating of 2400 for example, you should be having a Parry to Dodge ratio of 1.34:1 for example.