Glossary of Watch Terms.

tachymeter: ("tack IM eh ter") A feature found on some chronograph watches, a tachymeter (also called a "tachometer") measures the speed at which the wearer has traveled over a measured distance.

tank watch: A rectangular watch designed by Louis Cartier. The bars along the sides of the watch were inspired by the tracks of tanks used in World War 1.

telemeter: ("tel EH meh ter"): A telemeter determines the distance of an object from the observer by measuring how long it takes sound to travel that distance. Like a tachymeter (see "tachymeter"), it consists of a stopwatch, or chronograph, and a special scale, usually on the outermost edge of the watch face.

titanium: A metal that is used for some watch cases and bracelets. Titanium is much stronger and lighter than stainless steel. Titanium is also hypo-allergenic.

tonneau watch: A watch shaped like a barrel, with two convex sides.

U

unidirectional rotating bezel: An elapsed time rotating bezel (see "elapsed time rotating bezel"), often found on divers' watches, that moves only in a counterclockwise direction. It is designed to prevent a diver who has unwittingly knocked the bezel off its original position from overestimating his remaining air supply. Because the bezel moves in only one direction, the diver can err only on the side of safety when timing his dive. Many divers' watches are ratcheted, so that they lock into place for greater safety.