One problem Ive encountered is the differing target altitude values. Thats is to say, with each click of the mouse pointer directly over a field icon (without moving the pointer) I frequently get different altitude values.
Although Ive had great luck bombing generally, last night I was set up on a field with 3 B17s at 23k and calibrated excellently, to the best of my knowledge, but the damned sticks landed a good 1000 yrds past the targets.......