I,J,K, are functions of XYZ they refer to roughing allowance from the finished geometry to the roughing strokes. E.G. it sets back and out roughing strokes so at the end of G71 or G72 a final roughing profile can cleanup the strokes. It is similar to a G70 cleanup but with less control. Note I/X is in radius measure and K/Z should take into account offset that would screw up a trough or groove as in type II roughing