in the period from 1930 to 1933, milankovitch worked on the problem of numerical secular rotation pole movements. the earth as a whole he considered as a fluid body, which in the case of short-duration forces behaves as a solid body, but under an influence behaves as an elastic body. using vector analysis he made a mathematical model of the earth to create a theory of secular motion of the terrestrial poles. he derived the equation of secular trajectory of a terrestrial pole and also the equation of pole motion along this trajectory. the equations further led to a determination of the 25 most characteristic points with pole trajectories for both hemispheres. this mathematical calculation led milanković to 16 important points from the past that form parts of early explorations; 8 points triggered future explorations. he drew a map of the path of the poles over the past 300 million years and stated that changes happen in the interval of 5 million years (minimum) to 30 million years (maximum). he found that the secular pole trajectory depends only on the configuration of the terrestrial outer shell and the instantaneous pole position on it, more precisely on geometry of the earth mass. on this basis he could calculate the secular pole trajectory. also, based on milanković's model, the continental blocks sink into their underlying "fluidal" base, and slide around, 'aiming to achieve' isostatic equilibrium. in his conclusion about this problem, he wrote: for an extraterrestrial observer, the displacement of the pole takes place in such a way that the ... earth's axis maintains its orientation in space, but the earth's crust is displaced on its substratum. milankovitch published his paper on the subject entitled "numerical trajectory of secular changes of pole’s rotation" in belgrade in 1932.