With Patek Philippe Extract from the Archives confirming production of the present watch in 1891 and its subsequent sale on 6 December 1928. The Extract further states that the watch obtained a Geneva Observatory rating certificate in 1919. Also delivered with copies of the Geneva Observatory timing sheet and results of the 1919 First Class timing contest where the watch obtained an honorable mention with 706 points. Its movement had been prepared and adjusted by the renowned precision adjuster J. Golay-Audemars, one of Patek Philippe's best regulators of the time. Watches adjusted by him regularly excelled at timing contests.
In 1844 Antoine Patek began experimenting with detent escapements, producing pocket chronometers in exceedingly small numbers. One of them, no. 3218, was bought by Prince Albert at the 1851 London Exposition. These pocket chronometers were Patek Philippe's most precise watches and also among the most expensive to produce. It is believed that less than 60 of such chronometers were made, rendering them actually rarer than Patek Philippe's tourbillon watches.
These chronometers were manufactured either for the firm's most important clients or to be used for Observatory contests. Patek Philippe would keep the movements during a number of years for them to participate in different timing contest in the Observatories in Geneva, Kew or even Washington. From one Observatory contest to another, these movements were constantly improved to achieve even higher ratings. The present watch for example had been fitted with a Guillaume balance and double overcoiled balance spring for the 1919 contest. For the following trial, Patek Philippe used a bimetallic compensation balance with helical balance spring.
The participation at timing contests and the quest for constant improvement is also the reason why the present watch with a movement made in 1891 was not sold until 1928. These watches were exclusively reserved for Patek Philippe's most distinguished clients who often had to wait several years before finally receiving their much anticipated treasure - like this pocket chronometer. One of only three yellow gold open face examples of such chronometer with spring detent escapement to appear in public to date and furthermore preserved in excellent overall condition it is as much a trophy now as it was in 1928.
Other examples of Patek Philippe's pocket chronometer watches with spring detent escapement and helical hair spring are illustrated and described in Patek Philippe Museum - Patek Philippe Watches - Volume II, pp. 18-20.