The Sefer ‘Evronot is a Hebrew calendar book. The volvelles as well as hand diagrams and tables were some of the tools used not just for calculating and identifying pivotal dates and worshipping times for Jews, but also for ascertaining Christan holidays. This knowledge was a critical aid for protecting Jews from the danger posed by their having different worshipping times and habits from the dominant culture. The headings on the wheel denote the arrival of the new moon, which marks the start of the Jewish month, and the cycle of the sun. Whereas calendars appear in general to be a “convenient way to coordinate human movements with natural time,” as Elisheva Carlebach points out, the Sefer ‘Evronot demonstrates that the methods for doing so are culturally and historically shaped. The wheel, computing information with each push of a finger, demands interaction from the reader in order to yield knowledge not just to use, but to live by.