books.google.com - From the patristic age until the Gregorian calendar reform of 1582, computus -- the science of time reckoning and art of calendar construction -- was a matter of intense concern. Bede's The Reckoning of Time (De temporum ratione) was the first comprehensive treatise on this subject and the model and...http://books.google.com/books/about/Bede.html?id=yFsw-Vaup6sC&utm_source=gb-gplus-shareBede
