It is interesting to note that this wristwatch, #867849, chronologically follows Lot #584, #867848 - a rare coincidence!Similar watches are published in "Patek Philippe Wristwatches", by Martin Huber and Alan Banbery, 1998 Edition, p. 273-274.Ref. 1436Split-seconds chronograph wristwatches were "the must" of Patek Philippe technology and after 1938 were generally cased with this ReferenceThe majority are in yellow gold. Rarely, they are in pink gold, and only three stainless steel examples are known, two of which were sold by Antiquorum:- Geneva, April 10, 1994, lot 431.- Geneva, April 23 1995, lot 457.In the mid-1950's some were produced with a coaxial button on the winding-crown for the split-seconds functions (stop and reunite).What is a split-seconds chronograph?The split-seconds chronograph, in its present form, was first introduced in 1880. A split-seconds chronograph orrattrapante is a type of chronograph watch with two coaxial superimposed center-seconds hands that are controlled by two push-buttons. One push-button controls the split-seconds hand to stop or join the chronograph hand. The other push-buttons control both the hands and all of the functions of the chronograph. The two hands, the chronograph hand and the split-seconds hand, are used for timing several events that start simultaneously but are of different durations. To operate the split-seconds chonograph, both hands are started and remain superimposed. Then at the end of the first duration, the split-seconds hand can be stopped while the chronograph hand continues to move. The duration of the first event can be read. After recording, the split-seconds hand can be released to instantly move and join the chronograph hand, synchronizing with it and thus ready for another recording. At the end of each event the hands can be stopped and then returned to zero.