A watch displaying the day, date, month, and 24 hours that adjusts automatically for short and long months. An annual calendar requires only a single manual correction per year from the end of February to the 1st of March.
A watch showing the calendar without correction for a year, 1 March to 28 February.
A watch showing the day, date month and 24 hours, adjusting automatically for short and long months. The calendar needs setting only once a year - at the end of February to the 1st of March.
A watch feature that shows the day, date, month and time, adjusting automatically for short and long months.
Annual calendar is the feature that refers to a mechanical watch. It automatically adjusts months with 30 or 31 days and needs to be manually corrected when February turns into March. Thus it needs to be corrected once a year, which is why the calendar is called annual.