The most unusual feature of this watch is its return-to-zero mechanism, which is the only one known to date on a double-train independent seconds watch from the period. The idea of returning the center seconds hand to zero has been credited to Adolphe Nicole who patented his invention, applicable to a single-train mechanism, on May 14, 1862. It seems that Adrien Philippe worked independently in the same direction but concentrated his efforts on a double-train mechanism. His mechanism, though quie complicated, is very reliable and impressive when set properly. It implements a number of unusual features: a hairspring-like spring controlling the dead seconds, a continuous seconds hand concentric with the jumping fifth seconds one, and finally, a single button performing four functions: 1st push: activating. 2nd push: stopping. 3rd push: activating again and stopping both jump hands exactly at zero. 4th push while the hand is before zero: disengaging the stopping mechanism and allowing the chronograph to run continuously.The company was involved in the development of chronograph watches from the very beginning of its existence. By 1840 they had already made independent dead-seconds watches (for example. No. 274), based on the principle invented in 1776 by Moise Pouzait of Geneva, which, in later years, Philippe improved considerably. He moved the entire "independent" train over the center bridge, allowing more room for the going train and in particular for the balance, which is larger, affording better timekeepng qualities. He made important improvements regarding winding both movements by a single crown (Swiss patent No. 1017 of May 23, 1889) utilizing his earlier invention of a "free", or "slipping" mainspring, patented on June 16, 1863 in France.The hairspring-like control of the jump mechanism found in this watch was implemented by Patek Philippe as early as the second half of the 1850's (see Antiquorum, October 13, 1996, lot No. 509). The continuous second hand concentric with the chronograph one was constructed by Patek Philippe as early as 1856 (for example. No. 10051, now in the Patek Philippe museum).The watch offers an answer to the question of the purpose of two pinholes found on the center bridge of certain independent dead-seconds Patek Philippe watches: they were for mounting the endshake jewel plate, in case the watch was fitted with a return-to-zero mechanism. The endshake had to be minimized because there is very little room for the return-to-zero lever and there is an obvious need to equalize the increase of friction when the return-to-zero lever is engaged.From a historical and technological point of view, it is very important to have found this watch complete. It throws light on the struggle of early makers to solve the problem of the chronograph. It strengthens our respect for the Patek Philippe firm, of which one of the founding members, Adrien Philippe, was capable of inventing so complicated and ingenious a mechanism.