Equal Measure: The modern chronographs of Patek Philippe

On top of these technical improvements, caliber CH 28-520 also proposed a completely new method of displaying elapsed time. Instead of the standard chronograph subdials for the small seconds, 30-minute counter and 12-hour counter, this movement packs both the minute and the hour totalizers within one off-centered circular display at six o’clock. Two small co-axially mounted hands provide readings of elapsed time, while the chronograph seconds hand is centrally mounted, co-axial with the hour and minute hands, springing to action once the pusher is activated. Additionally, there is a day/night indicator discreetly contained within this display, increasing the overall functionality of the timepiece. Caliber CH 28-520 first appeared in the Ref. 5960 and the movement reference for this model is the caliber CH 28-520 IRM QA 24H, where IRM refers to indicateur réserve de marche and QA, quantième annuel, which tells us that the three apertures arching across the dial self-adjusts at the end of every month except on February 29, making this a later version of Patek’s annual calendar chronograph.