15th Century Calendar Keychain
- 50 Years Perpetual Calendar Keychain
- 15th century 50 Years Calendar Keychain
A perpetual calendar is a calendar valid for many years, usually designed to allow the calculation of the day of the week for a given date in the future.
For the Gregorian and Julian calendars, a perpetual calendar typically consists of one of two general variations:
14 one-year calendars, plus a table to show which one-year calendar is to be used for any given year. These one-year calendars divide evenly into two sets of seven calendars: seven for each common year (year that does not have a February 29) with each of the seven starting on a different day of the week, and seven for each leap year, again with each one starting on a different day of the week, totaling fourteen. (See Dominical letter for one common naming scheme for the 14 calendars.)
Seven (31-day) one-month calendars (or seven each of 28–31 day month lengths, for a total of 28) and one or more tables to show which calendar is used for any given month. Some perpetual calendars' tables slide against each other, so that aligning two scales with one another reveals the specific month calendar via a pointer or window mechanism.
The seven calendars may be combined into one, either with 13 columns of which only seven are revealed, or with movable day-of-week names.
An early example of a perpetual calendar for practical use is found in the manuscript GNM 3227a. The calendar covers the period of 1390–1495 (on which grounds the manuscript is dated to c. 1389). For each year of this period, it lists the number of weeks between Christmas day and Quinquagesima. This is the first known instance of a tabular form of perpetual calendar allowing the calculation of the moveable feasts that became popular during the 15th century.
Fine or Fashion: Fashion
- Metal color: Antique Gold Plated
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- Model Number: 1
- Metals Type: Zinc Alloy
- Material: Metal
- Gender: Unisex
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