A perpetual calendar knows the length of every month and the leap year, and runs without correction until 2100. What distinguishes this reference is how it says so: day, date and month in a single line across one aperture, which requires the discs behind that window to advance in unison rather than resolving into the three subdials the complication usually takes. 41.3mm platinum, gradient silvery dial in vertical satin. What matters on examination: that the in-line display steps cleanly at midnight with no lag between discs; that the leap-year indication sits correctly; and that the calendar has not been forced through a change while in its restricted hours. Confirmed through the desk. Maker: Patek Philippe. Reference: 5236P-011. Available through ELITA's private desk — verification review, discreet handling and storage. Price on request.