Historically notable, the present reference 902 desk clock features a large and conspicuous engraving on the back of the case reading "Jean R. Graef, August 16, 1968, Thank you for your friendship, Henri, Einar, Werner." According to research, it appears that Henri Stern, Einar Buhl, and Werner Sonn, the at-the-time top executives of Patek Philippe and the Henri Stern Watch Agency gifted this clock to Mr. Jean R. Graef who was a retailer of the brand in New York.
This reference 902 is from Patek Philippe's early series of table clocks fitted with a 17-ligne mechanical movement that is electrically driven and powered through the solar cells. The movement features a conventional lever escapement wound by speed-increasing gears, which are then activated approximately every 5 hours through an electric micro-motor. It is furthermore powered by an accumulator charged by the photoelectric cells (solar panel) on top of the clock’s case.
Watchmakers are always in quest of "free" sources of energy, but the disadvantage of light however is that it is not available around the clock.
Patek Philippe opened its Electronic Division in 1948 with the goal of exploring photoelectric, electronic, and nuclear timekeeping. The department produced the groundbreaking solar clock, the first of its kind.
In 1954, Patek Philippe patented its extraordinary photoelectric energy mechanism (Patent No. 298564). Photoelectric cells charged an accumulator which then powered a motor to wind a conventional Patek Philippe 17-ligne hand-wound pocket watch movement. With energy stored in either the accumulator or the movement spring, the firm claimed that the clock was capable of running in complete darkness for a year and with an accuracy of within 1-second per day.