The Lot of Basis, kleros baseos, also called the Lot of Foundation, is calculated from Fortune and Spirit together, taking the shorter arc between them and projecting it from the Ascendant, so that it stands as the single point in which the two principal lots are combined. It is read as the underlying support of the life, the base on which the whole rests, and in some Hellenistic material it is used in judgments about the length of life and the fundamental condition of the native. Because it depends on both of the primary lots it inherits their sect reversal twice over, and it is one of the points most likely to be calculated differently by different software; anyone comparing results should check the formula in use rather than assume agreement.
Because Basis draws on both principal lots, and each of Fortune and Spirit already reverses its own terms between a day and a night birth, the lot is sometimes described as carrying a double sect sensitivity, though in practice the shorter-arc construction from Fortune to Spirit, or Spirit to Fortune, projected from the Ascendant, is computed the same way regardless of sect once Fortune and Spirit themselves have been correctly placed for the birth in question; the sect reversal is fully absorbed into the two lots that feed it rather than applied a second time to Basis itself. This is a point of frequent confusion in modern software implementations, some of which apply an unwarranted additional reversal to Basis and so arrive at a different degree than the classical construction gives.