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Do you know your ‘quantièmes’? Quantième, of course, is French and means date function. There are numerous ways to monitor the date.

The most simple date function has only a date window, showing the numbers 1 to 31. Some watches indicate the date with a hand and a subdial, also with 1-31. For months with less than 31 days a manual correction is needed. The logical name for this complication is Quantième simple.

 

More complex systems shows more: the name of the day, which may be combined with the name of the month. In many cases manual correction for months with other than 31 days is required.
It will be evident that a mechanism that automatically takes all deviations from 31 into account (months with 30 days, February with 28, and in leap years 29 days) will be much more complicated than one which knows only months of 31 days. Such a mechanism, the Quantième perpetual (perpetual calendar) is a highly sophisticated complication, especially when it is combined, as is often the case, with a moon phase function. When a correction is needed, it is once in a century, for instance.

However, there are some variations between the relatively simple date function and the perpetual calendar. One of them is the Quantième annuel, which requires only one correction a year, for February. A version, with moon phases, was introduced in 1996 by Patek Philippe for lady’s watches and is highly successful.