A more recent attempt at a tooth profile redesign is shown in U.S. Pat. No. 4,823,638 to Ishikawa, wherein a tooth profile of the engaging splines is defined by a transformation of an original curve by the application of a reduced /2 scale to a corresponding similar figure, that is, a mapping curve derived by a similarity transformation from the movement locus of the crest of the flexspline relative to the circular spline