Abstract: A family of novel perpetual and multi-year calendars is obtained by various dispositions of four calendar data components, namely (1) calendar data comprising indications of the days of the month by number, (2) calendar data comprising indications of the days of the week by name, (3) calendar data comprising indications of the months of the year, and (4) indexing feature. The calendar data components are arranged in pairs on first and second display devices, one of which is movable relative to the other. The indexing feature in the perpetual calendar designs comprises a set of seven index positions and a movable index element locatable at any one of these positions. The indexing feature in multi-year calendar designs comprises a set of seven index positions labeled with calendar data including indications of the years by number.