From the patristic age until the Gregorian calendar reform of 1582, computus ? the science of time reckoning and art of calendar construction ? was a subject of intense concern to medieval people. Bede's The Reckoning of Time (De temporum ratione) was the first comprehensive treatise on this subject, and the model and reference for all subsequent teaching, discussion and criticism of the Christian calendar. The Reckoning of Time is a systematic exposition of the Julian solar calendar and the Paschal table of Dionysius Exiguus, with their related formulae for calculating dates. But it is more t