Tools Astrocalculator Precession module The Precession calculator module Precession This module is similar to the Apparent Coordinates module, but it only applies the effect of precession, not of nutation or aberration. To use the module, first enter the input coordinates and their epoch in the Original Coordinates section. You must also fill in the target epoch in the Precessed Coordinates section. Then, press the Compute button, and the object's coordinates, precessed to the target Epoch, are presented in the Precessed Coordinates section.