"The noted historian of science, George Sarton, called the eighth century 'The Age of Bede'. Bede wrote several major scientific works: a treatise On the Nature of Things, modeled in part after the work of the same title by Isidore of Seville; a work On Time, providing an introduction to the principles of Easter computus; and a longer work on the same subject; On the Reckoning of Time, which became the cornerstone of clerical scientific education during the so-called Carolingian renaissance of the ninth century. He also wrote several shorter letters and essays discussing specific aspects of computus and a treatise on grammar and on figures of speech for his pupils.
"On the Reckoning of Time (De temporum ratione) included an introduction to the traditional ancient and medieval view of the cosmos, including an explanation of how the spherical earth influenced the changing length of daylight, of how the seasonal motion of the Sun and Moon influenced the changing appearance of the New Moon at evening twilight, and a quantitative relation between the changes of the Tides at a given place and the daily motion of the moon. Since the focus of his book was calculation, Bede gave instructions for computing the date of Easter and the related time of the Easter Full Moon, for calculating the motion of the Sun and Moon through the zodiac, and for many other calculations related to the calendar. He gives some information about the months of the Anglo-Saxon calendar in chapter XV. Any codex of Bede's Easter cycle is normally found together with a codex of his 'De Temporum Ratione' " (Wikipedia article on Bede, accessed on 11-22-2008).
The first chapter of Bede's De temporum ratione liber entitled "De computo et loquela digitorum" (On Computing and Speaking with the Fingers) explained the method of finger reckoning which had evolved since the ancient world, as a reliable method, especially when a writing surface or writing implements were not available. Though the method was mentioned by classical authors such as Herodotus, no treatises on the topic survived, and it is thought that the technique was passed down mainly through oral tradition. Bede described "upwards of fifty finger symbols, the numbers extending through one million" (Smith, History of Mathematics  II, 200). Undoubtedly Bede's text, of which numerous medieval manuscripts survived, was influential on conveying the method during the Middle Ages.
Bede's De computo, vel loquela per gestum digitorum appears to have made its first appearance in print In Hoc in volumine haec continentur M. Val. Probus de notis Roma. ex codice manuscript castigatior . . . , ed. Giovanni Tacuino published in Venice by the editor,Tacuino, who was also a printer, in 1525. The editio princeps of De temporum ratione was published by Sichardus in 1529, four years after Tacuino issued his edition. Portions of De temporum ratione appeared in print as early as 1505, but these do not appear to have included the section on finger-reckoning. Smith, in his Rara arithmetica, stated that the 1522 edition of Johannes Aventinus’s Abacus atque vetustissima, veterum latinorum per digitos manusque numerandi contains a description of Bede’s finger-reckoning; however, this may be an error, since there was no record of this edition in OCLC or the Karlsruhe Virtual Catalogue when we searched the database in March 2013. Smith himself described only the 1532 edition of Aventinus’s work (see Rara arithmetica, pp. 136-138).
For a discussion of Bede's manual calculating methods see Sherman, Writing on Hands. Memory and Knowledge in Early Modern Europe (2000) 28-30.