Watch Glossary - D

D

Damascening - A method of decorating the bottom plate or bridges, consisting of a radial or striped design which appears to shimmer as it catches the light at different angles; especially associated with American watches from the 1870s onwards. It is actually a variety of engine-turning and unrelated to the damascening found in medieval weaponry, which is a technique of inlaying one metal in another.

Dart - A safety device incorporated into many lever escapements to prevent the lever and the roller from getting out of alignment. The lever carries a pointed prong, the dart itself, between the tines of its fork; this fits into a curved recess in a second roller, which restrains the fork if it happens to lose contact with the impulse-pin and prevents the lever from swinging clean out of engagement. The dart is chiefly associated with the European anchor-shaped lever and is rarely found in English side-lever watches.

Date - Ordinal number referring to a day of the month: the 10th February. Date-watch: watch indicating the date, the month and sometimes the year and the phases of the moon. Also called a calendar-watch or calendar. Perpetual calendar: watch indicating leap years as well as the date.

DD – day and date function

Deck Watch - A large precision-made watch used on board ship for synchronising chronometers with one another or conveying their readings to the deck where solar or lunar observations were performed. For this purpose it had to be easily carried from one part of the ship to another; it was therefore generally provided with its own case, unlike a true chronometer.

Decorated Movement - Some watch movements come highly decorated, for example with Geneva Stripes and blued screws. Whilst decoration may not improve function, it often indicates a degree of hand assembly/finishing and an attention to detail in the construction of a watch. Some watches show off the decorated movement through the use of a display back.

Detached - Of an escapement: having a separate unit introduced between the escape-wheel (or the final wheel of the train) and the balance, so that the two are in contact only when the specific processes of impulse and locking require them to be so. Usually applied to the lever escapement, whose full name is ‘detached lever’ (to distinguish it from the rack-lever). Lever watches dating from the 1820s, when this system was still a novelty, sometimes have the word DETACH'D engraved on the cock-foot.

Detent - In an escapement, a separate component between the balance and the escape-wheel which performs the locking function, so that the balance itself does not have its freedom of movement impaired by the need to do this. The detent may revolve (pivoted detent) or it may consist of an arrangement of flat springs (spring detent); the latter, devised almost simultaneously by Arnold and Earnshaw in about 1780, was for many decades the standard chronometer escapement.

Dial - Indicating "face" or plate of metal or other material, bearing various markings to show, in ordinary watches and clocks, the hours, minutes and seconds. Dials vary verymuch in shape, decoration, material, etc. The indications are given by means of numerals, divisions or symbols of various types.

Digital – digital time indication

Digital Display - As opposed to an analogue display, a digital display shows the time in numbers. Most often used with LCD displays in the case of a quartz watch, during the 1960's there were many mechanical digitals with rotating discs instead of hands. Cut outs in the dial would show the correct time. The first quartz digital watches came onto the market in the early/mid 1970s; for example the Pulsar Time Computer.

DIN - Deutsches Institut fur Normung

Direct-Drive - Refers to a seconds-hand that moves forwards in little jerks. Trotteuse, French term for a direct-drive seconds-hand, especially a centre seconds-hand.

Display - Indication of time or other data, either by means of hands moving over a dial (analogue display) or by means of numerals appearing in one or more windows (digital or numerical display); these numerals may be completed by alphabetical indications (alphanumerical display) or by signs of any other kind. Example: 12.05 MO 12.3 = 12 hours, 5 minutes, Monday 12th March. Such displays can be obtained by mechanical or electronic means.

Diver's Watch - Divers' watches traditionally are large, featuring a graduated rotating bezel and often a screw down winding crown. Water resistant to 200m as a minimum, the modern diver's watch must confirm to certain standards laid down for example by ISA in order to be classified as a Scuba Divers Watch.

Dome - The fixed inner back cover of an English consular case, pierced with an access hole for the winding-key.

Double roller escapement - A variety of lever escapement in which the balance-staff carries two rollers: one carrying the impulse-pin and the other with a recess which engages with the safety dart.

Draw - A configuration of the locking face of a pallet which causes it to pull the escape-wheel more tightly into engagement during the locking process, producing infinitesimal recoil in the train. The purpose of this is to prevent pallet and escape-wheel from slipping out of engagement.

Drop - The interval between impulse and locking during which the escape-wheel, and therefore the whole train, is free to turn.

Duplex escapement - A complex escapement invented by Pierre le Roy in about 1750 but favoured chiefly by English watchmakers in the first half of the following century. The escape-wheel has two sets of teeth (hence the name): short ones for impulse, engaging with a cam on the balance-staff, and long ones for locking engaging with a tiny ruby roller (which tends to wear) likewise mounted on the balance-staff.

Dust Cap - (or dust-cover). A protective cover fitting over the bottom plate and sides of a movement, with holes cut in it for the winding-key and (usually) the table of the cock. In English watches it is of gilt brass, removable and secured by a sliding catch; French and Swiss watches occasionally have silver dust-caps hinged to the movement.