Originally Posted by

**jere**
Booi,

Taking the derivative gives you the instantaneous value. Like I was saying earlier, the derivative is taken over infinitesimally small steps (much smaller than 1%).

Inverting those points assumes that the DR rate at X% parry is the same value of DR rate at (X+1)% parry, which really isn't technically the case. The DR rate at X+1 is worse than at X, though only slightly, so you will see that the actual number will end up being lightly higher than what you calculated. I was trying to allude to this in my previous post.