It should be noted that after Shear Cutters (PDC) were introduced the main change in our math models were in the two dimensional area of a circle for a given C cut and P penetration. The result of using a SHEAR cutter is the basics of 5 times less A area for a given C cut (2D segment of a circle versus 3D segment of a sphere) and the different strength of the rock when sheared versus being compressed.