The present openface pocket watch is a shining example of early 20th-century horology and the innovative technical skills demonstrated by the famed brand Patek Philippe. At first glance one may see a time only watch, however the movement is marked “Extra” a designation applied only to watches that have undergone even more rigorous testing, refinement, or enhancement beyond the brand’s already high standards. Upon close inspection of the escapement, one notes the use of a Guillaume balance wheel with blued steel hairspring – the state-of-the-art at the time, used for the finest watches where precision timekeeping was of utmost importance.

Charles-Édouard Guillaume won the Nobel Prize in Physics in 1920, making significant contributions horology with his work on various nickel-steel alloys such as Invar and Elinvar. Guillaume balances with bimetallic rims made of Invar and brass, when used with blued steel hairsprings, are remarkably stable across a range of temperatures.

The present watch from circa 1915 is a wonderful example of the commitment to precision and accuracy in fine Swiss watchmaking. The engraving on the movement indicates the watch was retailed by Wm. Senter & Co., a watchmaking firm located in Portland, Maine. William Senter (1850-c. 1926) apprenticed first to his uncle in 1870, also William Senter (1813-1888), and after his uncle's death in 1888, carried on their family business. As engraved on the cuvette, the “Extra”-grade movement was awarded “Awarded Honourable Mention Geneva Astronomical Observatory Timing Contest 1915-1916”. With a flawless enamel dial, it is offered in wonderful overall condition.