BRÉQUET, ABRAHAM LOUIS—A celebrated Swiss mechanician and watchmaker born at Neufchatel in 1747. He made several improvements in watches, the most notable being the Bréquet hairspring still in use in the best watches. He died in 1823. [Illustration: BRÉQUET SPRING] BRÉQUET SPRING—A form of balance spring which is a volute with its outer end bent up above the plane of the body of the spring and carried in a long curve towards the center near which it is fixed. Like all other springs in which the outer coil returns towards the center, it offers opportunities of obtaining isochronism by varying the character of the curves described by the outer coil and thus altering its resistance. So-called from its inventor, Abraham Louis Bréquet (q. v.). Its advantage over the flat spring is that the overcoil allows expansion and contraction in all directions, thereby avoiding a good deal of side friction on the pivots as well as insuring more nearly perfect isochronism in changes of temperature. BRIDGE—A standard fastened to the plate, in which a pivot works. BRIDGE MODEL—The term given to watch movements in which plates or bridges carrying the upper pivots of the train rest firmly on the lower or dial plate and are held rigid by steady pins on lower side of the plate; the bridge being secured direct to the dial plate by screws termed plate or bridge screws. This is the most common construction of present-day manufacture and is utilized in three-quarter plate or separate and combination bridges covering one or more pivots of train wheels. Its alternate is "pillar model." BUCK, D. A. A.—A watch repairer in Worcester, Mass., who designed a model for the Waterbury watch. His first model was not successful, but in 1877 he completed one which, a little later, the Waterbury Company, with Buck as master watchmaker, started to make. He remained with the company until 1884. BUSH—A perforated piece of metal let into a plate to receive the wear of pivots. BUTTING—The engaging of the tips of the teeth of two wheels acting in gear. The proper point of contact being in the line of the shoulders of the teeth, butting is remedied by setting the wheels farther apart. BUTTON—The milled knob used for winding and setting a keyless watch. CALCULAGRAPH—Trade name for a device for automatically computing and recording elapsed time in connection with factory jobs and other work where it is necessary to show the amount of labor used. CALENDAR—A system of dividing the year into months and days. The principal calendars known to history are: the Julian calendar; the Gregorian calendar; the Hebrew calendar; the Mohammedan calendar; and the Republican calendar. None of them has been quite accurate in dividing up the solar year, and frequent arbitrary corrections are necessary to secure a practical approximation. See descriptive article under each title.