Annual calendar
"A full or partial simple calendar that takes automatically into account months with less than 31 days, but not of leap years. It must be adjusted once a year. " (FHH)
There are exceptions between different annual calendars but a general rule is a calendar which indicates the different length of each month automatically jumping to the 1st after the 30th or 31st of the previous month, either with the exception of February or, if including February with 28 days then excluding the leap year.
An annual calendar can often not be recognised visually by the dial, being able to correct between the lengths of months and actually being an annual calendar.
Blancpain Quantième Annuel GMT
Laurent Ferrier annual calendar
Patek Philippe annual calendar (Image courtesy of Christies auction house)
(Bissextile = Leap year)
Perpetual calendar (QP-Quanitiéme Perpetual)
"Device that changes the date at the end of each month including the 29th February in leap years." (Berner)
"Devised to incorporate the specificities of the Gregorian calendar. It is perpetual because it automatically adjusts to months with 30 days and to the 28 or 29 days in February. For this, it incorporates a mechanical memory whose sequences are repeated every 48 months to correspond to the cycle of leap years. It must only be adjusted for the exceptionally non-leap year years, the next being 2100 and 2400." (FHH)
A classical QP dial, the month hand turns once in 4 years. (Bissextile=Leap year)
The majority of QP’s indicate day/date/month/year in sequence
Here the year hand turns once every two years. (L=Leap year)