Functions of the Single Wheel Watch. The “single-wheel” of 60 sharp ratchet teeth is mounted in the center. It delivers an impulse to the impulse pallet fitted to the arbor of the escape lever. This lever is fitted with three racks; the inner one drives the seconds hand pinion, the outer racks, mounted one over the other, are for the impulses. The top one delivers an impulse to the top pallets of the balance for 30 seconds directly from the torque received from the “single wheel”, the lower one in the opposite direction for the next 30 seconds. The direction-switching mechanism has its own escapement; when the “single wheel” drops off the arbor of the escape lever it pushes a lever which in turn allows the arbor to drop down and thus engages the lower rack with the lower pallets of the balance wheel. After that the “single wheel” locks itself on a pivoted detent. The arbor of the escape lever is attached to a fusee-like chain and terminates on a spring-loaded half pulley. During the 30-second impulse by the “single wheel”to the escape lever arbor, the chain winds around the arbor. The energy thus stored in the pulley's spring, via the chain, gives enough torque to the escape lever for 30 seconds in the opposite direction. Thus, for the impulses in this direction, the escapement is a constant force one. In this phase the “single wheel” is locked on a pivoted detent. At the end of the phase, that is after 30 seconds, the unlocking pallet also mounted on the escape lever arbor unlocks the detent and the “single wheel” drops off on the impulse pallet of the escape arbor. During this dropping it lifts a lever which in turn lifts the escape lever arbor and switches back to the top racks and top pallets of the balance wheel. The single wheel is ready to deliver an impulse in the opposite direction.The motion mechanism, which in an ordinary watch would be a motion train, is equally unconventional. The extension of the “single wheel” which rotates once per hour is fitted with a friction-fit tube with a pallet at the base. The square top of the tube is for the minute hand. The pallet lifts a lever connected to another which is fitted with a spring-loaded click that slides on arms of the 12-arm hour star. When the lever drops off the pallet, the energy in the spring instantaneously returns the click lever to its rest position which bring along one tooth of the star making the hour hand jumping one hour.History of one-wheel clocks and watches.The first “unconventional” horologists who dared to try the idea were Julien LeRoy and Jean-André Lepaute two of the greatest names in French horology at the time. As Thomas Reid wrote in 1826 in his “Treatise on Clocks and Watch Making”, Lepaute and LeRoy initiated a trend for unconventional clocks with one wheel only, which did not catch on because there were no horologists skillful enough to execute the clocks. In 1751 Lepaute presented a single-wheel clock of his invention to Louis XV. Both Lepaute and LeRoy employed the idea only in clocks and made very few of them. We have only one ever seen one and have heard of another.In 1773, William Small of Birmingham, member of the Lunar Society, patented a single-wheel clock.In 1774 James Ferguson designed and published an idea for a clock with one wheel “by means of a double escapement”. To our knowledge none was ever made.There exists a one-wheel clock, circa 1850, with torsion pendulum, which is attributed to Silas Burnham Terry (ca. 1800 1876) of Thomaston, USA. We know that Terry made torsion pendulum clocks, and it is conceivable that the clock is his experimental model. Around 1893 Nowman M. Saati from Providence patented (British patent of January 9, 1894) and made a single-wheel marine chronometer. The clock is in a private collection. Only three watches with a single-wheel are known: this one, another by Gautrin, numbered 1 9/97, in the Geneva Musée de l'Horlogerie et de l'émaillerie and one made by Saati based on the same principle as his marine chronometer mentioned above, now in a private collection. Conclusion : In the field of technical horology, it is extremely rare to see a mechanism so unusual, so unconventional and so complicated. It has only one wheel but two escapements, changes the direction of the escapement, delivers constant force impulse in one direction, and features an inovative lever-based motion mechanism. When Ferdinand Berthoud and Jean-Baptiste LeRoy examined Gautrin's mechanism in 1796, they called it “ingenious”. The idea of making a movement based on a single wheel is daring in itself, but to do it in such a way that the direction of the impulse to the balance changes every 30 seconds is so unconventional that it is difficult to imagine a traditional horologist even considering such a possibility the torque delivered to the escape racks changes its direction every 30 seconds. This is what distinguishes geniuses from ordinary people they are able to put into practice ideas that others find utopian and they find solutions never thought of before. Pierre-Laurent Gautrin did just that. His invention became an instant object of admiration. Horological experts wrote about it for many decades after it was made as a marvel of ingenuity in watchmaking. In 1796, the Institut National des Sciences et Arts a name given to the French Academy of Sciences by the revolutionary government - praised the watch and awarded Gautrin a prize of 300 francs. To America the news came rather late, in 1885, when the May issue of the Jeweler's Circular Keystone p. 128 informed its readers about Gautrin and his single-wheel watch. As late as 1903 it was mentioned in the Almanach des horlogers, p. 35. Eventually, an entire book was written about it:“Montre à une roue”, by Yves Droz and Joseph Flores, France, 1998. Pierre-Laurent Gautrin (before 1755- January 2, 1823 Paris).Trained as a casemaker, received as a master on September 3, 1767. He established himself at the Cour du Palais, where he was listed as early as 1768. He is recorded in the Place Dauphine in 1772. On August 23, 1786 he declared bankruptcy but continued to practice his profession. In 1806 he retired to Ermenoville. 1797-98 he published a memoir on two seconds watches.1799 he presented a one wheel watch for a prize and stated that he also sold one 15 years previously to Louis XVI.*. Double face watch with astronomical indications in Worshipful Company of Watchmakers in London.* Coach watch in Brussels Museum with a balance placed vertically. Literature:Journal Suisse d'Horlogerie, vol. IX, July, 1884, pp. 1-7.Jeweler's Circular Keystone, May 1885, p. 128.Almanach des horlogers, for 1903, p. 35.Antiquarian Horology, Vol. 5 1966, p. 169.Horological Journal, August 1995, p. 271.Montre à une roue, Yves Droz and Joseph Flores, France, 1998.Treatise on Clocks and Watch Making, Thomas Reid, Edinburgh, 1826.AWCC Bulletin, December 1953, p. 53.“Les Ouvriers du Temps”, Jean-Dominique Augarde, Antiquorum Editions, Geneva, 1996, pp. 96, 322.Saati's handwritten notes, private collection.