specifying the limits within which the answers lay. Known as the method of exhaustion, Archimedes employed it in several of his works, including to approximate the value of π (Measurement of the Circle), and to prove that the area enclosed by a parabola and a straight line is times the area of a triangle with equal base and height (Quadrature of the Parabola). Archimedes also showed that the number of grains of sand filling the universe was not uncountable, devising his own counting scheme based on the myriad, which denoted 10,000 (The Sand-Reckoner). The most characteristic product of Greek mathematics may be the theory of conic sections, which was largely developed in the Hellenistic period, starting with the work of Menaechmus and perfected primarily under Apollonius. The methods employed in these works made no explicit use of algebra, nor trigonometry, the latter appearing around the time of Hipparchus. Ancient Greek mathematics was not limited to theoretical works but was also used in other activities, such as business transactions and in land mensuration, as evidenced by extant texts where computational procedures and practical considerations took more of a central role. Transmission and the manuscript tradition Although the earliest Greek language texts on mathematics that have been found were written after the Hellenistic period, many of these are considered to be copies of works written during and before the Hellenistic period. The two major sources are Byzantine codices, written some 500 to 1500 years after their originals, and Syriac or Arabic translations of Greek works and Latin translations of the Arabic versions. Nevertheless, despite the lack of original manuscripts, the dates of Greek mathematics are more certain than the dates of surviving Babylonian or Egyptian sources because a large number of overlapping chronologies exist. Even so, many dates are uncertain; but the doubt is a matter of decades rather than centuries. Netz has counted 144 ancient authors in the mathematical or exact sciences, from whom only 29 works are extant in Greek: Aristarchus, Autolycus, Philo of Byzantium, Biton, Apollonius, Archimedes, Euclid, Theodosius, Hypsicles, Athenaeus, Geminus, Hero, Apollodorus, Theon of Smyrna, Cleomedes, Nicomachus, Ptolemy, Gaudentius, Anatolius, Aristides Quintilian, Porphyry, Diophantus, Alypius, Damianus, Pappus, Serenus, Theon of Alexandria, Anthemius, and Eutocius. The following works are extant only in Arabic translations: Apollonius, Conics books V to VII Apollonius, De Rationis Sectione Archimedes, Book of Lemmas Archimedes, Construction of the Regular Heptagon Diocles, On Burning Mirrors