A written calendar, then, is not so much as a cognitive tool to assist the reckoning of time, but a cognitive and cultural tool that can either promote social coordination or intersubjective senses of uncanniness, or even both, as in the case of the Jewish calendar. Calendars as artifacts are tools of power and social coordination. There also is an important contrast between complex calendars that require trained experts to interpret them versus simple calendars that almost anyone can use. The former are associated with astrologers. In Hinduism, the ability to chart the multiple cycles in the sky is important and involves trained specialists. In contrast, the Gregorian calendar requires very little specialized knowledge to use. . . . The manner in which the Gregorian calendar mediates the different logics of Hinduism, Islam, and Judaism is to represent holidays in those faiths as moving -- a cognitively useful, even if not entirely fair or accurate, representation. Objects of time think for their users, but the manner in which the Gregorian calendar thinks for non-Christians is not always useful to those non-Christians. What is useful in one respect is not functional in another. -- pp. 96 - 98.

Expert versus Lay Calendars — Thoughts from “Objects of Time”