Can someone please tell me the methods used in astronomical retro-calculation? I have put posts up about the n body problem, lunar perturbations, and Ptolemy's eclipses, but I need to know explicitly the methods used to determine, for example, whether or not a Babylonian tablet is reliable based on its astronomical observations. Essentially you would rewind a model of the solar system (including the moon for ancient lunar observations) to the BC date, and compare the coordinates to the observations given on the tablet. But what theories exist for that? The n body problem can at best be approximated, and approximations of solar system coordinates based on circular orbits, like the former, would diverge over long periods of time. I desperately ask again: What are the methods used in astronomical retro-calculation?