It is therefore essentially a mathematical work on the sphere and Recorde certainly read works by Ptolemy, Proclus, Sacrobosco and Oronce Fine before writing his text.
Ito kaya ay mahalagang isang matematiko sa trabaho ang sakop at Recorde tiyak read gumagana sa pamamagitan ng Ptolemy, Proclus, Sacrobosco at Oronce Fine bago magsulat ng kanyang teksto.