This watch is one of the exceedingly rare sports timing watches made by Patek Philippe. It is interesting to note that this highly exclusive niche product features the well-known 13''' chronograph movement, used in all chronograph wristwatches of the period. It is also fitted with a superb and beautifully tropicalized black lacquered dial on which all scales and the signature are in "negative". In fact, whereas traditional dials have a background colour with scales and signatures printed on top, the present technique features the dial colour as a layer above the silvered background, allowing the scales to shine through. This technique of dial making must be regarded as the ultimate state of the art in postwar dial manufacturing.
The dial's design is laid out to allow best readability of the elapsed time and the indications on the subsidiary dials. While timing an event with the watch in hand, the applied silvered hour markers appear black due to a mirror effect, thus becoming invisible against the black dial. Thanks to this elaborate system, the timekeeper can fully concentrate on the scales without being influenced by the hour indication.
The pendant to six o'clock is designed for the wearing of the watch suspended from a cord around the neck, the water-resistant two-body case with screw back protects it from weather while timing outdoor events. In fact, this model here must have been the only ever made reference of a pocket watch at Patek Philippe featuring a screw back case.
Reference 840 was in production from 1951 until the late 1960s and according to research, a small series of only around 30 examples was made. This watch is believed to be one of less than 10 examples of this reference to appear in public to date and the only example known with tropicalized dial.
For other examples see: Patek Philippe Steel Watches, John Goldberger, 2010, p. 28-29; Patek Philippe, Huber & Banbery, 1982, p. 189; Patek Philippe Museum Volume I, 2013, p. 313.