B. Measure total height of rear sight from top of barrel..
C. Add “A” + “B”
D. Measure barrel diameter at the front sight blade and divide by 2.
E. Subtract “D” from “C”. This is the total height of front ramp and front sight required.
F. Measure height of any existing ramp from bottom of dovetail to the top of the barrel
G. Subtract “F” from “E” This is the height of the blade required to fit an existing front sight ramp.
Photo Credit: http://www.flickr.com/photos/simonov/351717236/sizes/s/in/photostream/