For decades, split-seconds chronographs that allow lap times to be measured without interrupting an ongoing event time measurement have ranked among the most coveted Patek Philippe specialties. That was already the case in the 1920s, when the manufacture not only presented its first wristwatch chronometer but added the rattrapante function right from the start.

For the first time, the Ref. 5370 incorporates the calibre CHR 29-535 PS in its pure form without the added complication of a perpetual calendar. With the Ref. 5370, Patek Philippe also extended its range of pure split-seconds chronographs with a two-pusher model, a stopwatch with two pushers for the basic start, stop, reset functions and an additional on/off button in the crown for the split-seconds function.

Patek Philippe - Chronographe à rattrapante référence 5370

Split-seconds chronograph Ref. 5370. © Patek Phillipe

The calibre CHR 29-535 PS movement, developed and crafted in-house, melds tradition with innovation. Its traditional facet is the underlying concept of a manually wound movement with column-wheel control and a horizontal wheel clutch that remains the benchmark for many friends of mechanical watches. To preserve this heritage in the 21st century, it was optimized in many respects and endowed with patented innovations:
- Clutch wheels with patented tooth profiles boost efficiency in power transmission and reduce wear.
- The mesh depth of the clutch wheels is not adjusted with an eccentric next to the clutch lever; this is done much more precisely and easily with an eccentric column wheel cap at the outermost end of the clutch lever.
- Self-adjusting hammers in jewel bearings simplify the servicing procedure.
- The brake lever that stops the chronograph wheel is directly synchronized with the clutch lever.
- The slotted minute-counter cam coasts the chronograph and split-seconds hands to a stop rather than abruptly blocking them.

These new features of the mechanical chronograph are joined by innovations dedicated exclusively to the rattrapante function:
- When lap times are stopped, a newly designed isolator uncouples the split-seconds wheel from the chronograph wheel to eliminate unwanted friction and prevent a degradation of balance amplitude while the split-seconds hand is immobilized.
- The split-seconds lever that positions a ruby roller between two flat heart cam shoulders keeps the chronograph and split-seconds hands precisely aligned as long as they are superposed.

Patek Philippe - Chronographe à rattrapante référence 5370

Split-seconds chronograph Ref. 5370. © Patek Philippe

A glance at the dial illustrates what in Geneva is deemed functional beauty: fast and exact legibility without unnecessary embellishments that distract from the essence. Thanks to slender leaf-shaped hands with luminous coatings as well as the applied Breguet numerals in white gold, the time is eminently readable. Stopped times are also superbly legible with the slender chronograph and congruent split-seconds hands in rhodiumed steel as well as the instantaneous 30-minute chronograph counter hand in white gold and the white printed scales that stand out prominently against the black background.

Enamel dials challenge the skills of the dialmakers to the extreme. The solid white-gold dial of the Ref. 5370 split-seconds chronograph is first coated with black enamel by hand. The coating is melted in an oven at 850°C and then allowed to solidify to a glasslike consistency by controlled cooling. The result is an intense black that preserves its depth and gloss across centuries.

Patek Philippe - Chronographe à rattrapante référence 5370

The Split-seconds chronograph Ref. 5370 bears the Patek Philippe Seal, © Patek Philippe

The CHR 29-535 PS calibre comes in a platinum case of befitting stature. The watch is mounted on a hand-stitched alligator leather strap with large square scales, and a platinum 950 fold-over clasp.