Geometry means earth measure, needed to determine longitude accurately, and certainly evident in the Song Dynasty Map of 1137 a. d. showing the long sinuous courses of the Yellow and Yangtze rivers with such accuracies that precise longitude measure had been employed (the Song Dynasty Map probably copied from ancient sources maps by perhaps Xia dynasty leaders Yu and Shun), and that precision only by having measured the earth’s axial precession rate (see Page titled Great Pyramid for Navigation).
