27
ENGLISH
The perpetual calendar has a mechanism that
takes into account the length of the current
month (28, 30 or 31 days), and counts a 29th
February every leap year. The date, day of the
week, month, year, and moon phase are therefore
indicated mechanically, without the slightest
need for readjustment until 1 March 2100.
All these are interlinked by the ingenious
mechanism of a genuine, entirely mechanical
programme: merely changing the initial date
thus eects the appropriate changes in all
other functions.
Our time measurement is based on the
Gregorian calendar, i.e. a year of 365 days,
5 hours, 48 minutes, and 46 seconds, or
in decimals, 365.242192 days. In practice,
the yearly excess of just less than a quarter
(0.242192) of a day is corrected by the 29th
February in leap years. The few missing
decimals are then compensated for every 100
years, by excluding 29th February.
For the sake of greater precision, this exclusion
does not take place when the number of
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