The lineage of all Patek Philippe perpetual calendars can be traced back to the pocket watch ref. 725 which was introduced in 1940. We are looking for the series introduced in the 1970s: ref. 725-4 which has a linear perpetual calendar, otherwise known as the ‘American straight line calendar’ (which refers to a single aperture opening that shows the month/date/day). Please let us know if you have one of these pocket watches and you would like to sell.
