Patek Philippe Nautilus Annual Calendar Ref. 5726/1A
A watch equipped with an annual calendar mechanism correctly indicates the dates of all 12 months where manual intervention is only required once each year.
This is unlike standard date display mechanisms that will run out of sync five times a year. This is because either the date disc or the date pointer will indicate all 31 consecutive dates of the month, from 1 to 31, before beginning a fresh cycle.
As there are five months in a year with fewer than 31 days, it simply means that the standard date mechanism has to be manually reset five times in a year. Excluding February, the other four months, April, June, September and November, have 30 days.
What is required for an annual calendar mechanism is to have the date indication corrected on 1 March every year. February is a peculiar month as it will have 28 days during non-leap years and 29 days during a leap year.
Patek Philippe popularised the annual calendar function with its Reference 5035 that was launched in 1996. This was regarded as the first annual calendar wristwatch. Apart from the date display, the Reference 5035 also has day and month pointers. More wheels and pinions are used rather than rockers and levers for Patek Philippe’s annual calendar mechanism.
The calendar we are all well familiar with is based on the creation of Romans that has evolved into what it is today. Though the ancient Roman calendar was based on the lunar calendar where the New Moon meant the first day of each month, they eventually evolved it into a solar calendar to better represent the four seasons. A year then was 10 moons long. In other words, a Roman year was 10 months long while the winter season of around 60 days wasn’t considered part of the calendar.
There are four months of our current calendar named after their Latin numerical chronological sequence: September, derived from “septem” for “seven”, October from “Octo” meaning “eight”, November from “novem” or “nine” and December from “decem” that means “ten”.
It obviously sounds odd but the names of these names are from the ancient 10-month Roman calendar. Two additional months, January and February, were later added to the Roman calendar and placed after the religious year to account for the unclassified 60 days. In around 450 B.C., January was regarded as the beginning month of the year, followed by February.