TRAIN. The wheels and pinions which connect the going barrel or fusee with the escapement. In watch work, the wheel is the driver and the pinion the follower, except in the motion work. The 'going train' concerns the timekeeping part of the mechanism, the 'striking train' that side concerned with the striking. In the case of a fusee watch, the great wheel, and in a going barrel watch the teeth round the barrel, drive the centre pinion, to the arbor of which is attached the centre whee]. This drives the third wheel pinion, the third wheel driving the fourth wheel pinion, the fourth wheel driving the escape wheel pinion. The number of teeth in the various wheels and pinions in general is determined by the following considerations (among others): The minute hand, being fixed to the centre wheel and pinion arbor, must make one revolution in an hour. The fourth wheel, to the arbor of which the seconds hand is fixed, must make one revolution in a minute.

TRIAL NUMBER. A symbol used to express the relative excellence of chronometers and watches in competitive trials. The Greenwich Observatory method was to multiply the difference between the greatest and the least variation by twice the difference between one week and the next.

TRIPLE-CASED. A watch, usually made for the Turkish market, which has an additional case to the outer case of a pair-case watch.

TRIPPING. The accidental passing of two teeth of the escape wheel instead of one. This may occur in the duplex and detent escapements.

TURKISH MARKET WATCHES. Watches made for export to Turkey and provided with a dial with 'Turkish' numerals. Such watches normally had three cases; that over the movement being plain, the second with some engraving to the rim and the third or outer tortoiseshell-covered or occasionally sha-green. A fourth case, either of stiffened leather or silver, of native craftsmanship, is sometimes found. Watches were exported to Turkey in the 17th century, but large quantities were made in London for this market at the end of the 18th and early 19th centuries.

TWO-PIN ESCAPEMENT. See SAVAGE TWO-PIN.