Perpetual calendar from the 1900's with its patent

This perpetual calendar is a patent of late Vince Farkas, issued in 1900 as the photocopy of the original patent shows. The patents number appears on the "neck" of the medal 17922. Although the patent shows the calendar with Hungarian text, the medal offered here has German text. The medal shows wear but it is rare in this form.

Obverse: Shows the length of day and night and the rise and sunset times of different months. On the outer rim the name of month appear, that you can set and read the data respectively.

Reverse: The days of week and dates

Metal: some metal, I cannot identify

Diameter: 26mm (1")-32.5mm

Weight: 8.3gramm

I have seen similar perpetual calendar but they omit the patent number, so it would be interesting to find out, which is the copy of which. A very interesting project for calendar medals collectors. I will send also the copy of patent if you wish,
A similar design was auctioned here:
It is interesting how Vince Farkas could get a patent for an existing design.
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

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 of two sets of seven calendars: seven for each common year (year that does not have a February 29) that starts on each day of the week, and seven for each leap year that starts on each 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. [1 ]

The seven calendars may be combined into one, either with 13 columns of which only seven are revealed, [2 ][ 3] or with movable day-of-week names (as shown in the pocket perpetual calendar picture.

Note that such a perpetual calendar fails to indicate the dates of moveable feasts such as Easter , which are calculated based on a combination of events in the Tropical year and lunar cycles. These issues are dealt with in great detail in Computus .

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 which became popular during the 15th century. [4 ]

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