Rather than take means of individual observations as a normal practice, or try to make the theory fit all the observations, as Hipparchus does, he allows theory to confront the set of all observations in a more holistic fashion. This means that the observations to be exhibited are chosen, to some extent, in accordance with the theory. So older observations may be selected, or adjusted, in accordance with what the theory predicts.23 It is a dangerous practice, but arguably necessary within reasonable limits. It is allowed in modern statistics under the name rejection of outliers, to deal with
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