Calendars

1. There are only 14 different annual calendars.
2. There are only 28 different monthly calendars.
3. A calendar for a particular year can be reused after 6, 11 or 28 years, depending on the remainder obtained by dividing the year by 4.

These properties are easy to observe and can be the subject of an investigation that combines knowledge of the earth-moon-sun system with mathematics and history.

The calendars kit shows three different perpetual calendars, each for the period 1901-2099. The calendars are the (modified) Servois calendar, a circular calendar and the strip calendar, which can be made into an elegant desktop model by students. Student kits are made of card, while the teacher model is made of acrylic with magnets at the back.

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