 Heytesbury, however, remains in the framework of Aristotelian philosophy of nature, and the problems he discusses are to be found in Aristotle’s Physica and De caelo. Nevertheless, Heytesbury is captivated by the mathematical approach es the earlier Oxford Calculators. Like Thomas Bradwardine and Richard Kilvington, he examines physical problems using mathematical apparatus. In Chapters 4–6 of the Regulae, Heytesbury develops measurement by limit, i.e., by the first and last instants of beginning and ending, and by the intrinsic and extrinsic limits of passive and active capacities. Although these types of “measuring” do not appear to be straightforwardly mathematical, they provide the basis for mathematical considerations and give excellent results in analyses of the instantaneous motion, as well as continua. As Wilson states: