The greatest angular displacement a balance moves – measured from the zero or rest Position to position of maximum displacement, expressed in degrees.

Abraham Louis, 1747 – 1823 Horological genius / inventor. The name given to the type of balance spring which has its outer coil raised above the body of the spring & curved inwards.

A watch with hands that display hours, minutes and seconds, together with an additional mechanism for measuring continuous or interrupted periods of time and set to zero independently of the watch movement.

A watch that has obtained a certificate from an official neutral testing center such as “COSC” (Controle Officiel Swiss des Chronometres) or “SOCC” (Swiss office for chronometric controls) after having passed strict precision tests for accuracy. These tests are performed in a laboratory over a minimum 15-day period. They test the movement alone, using successive daily rate figures at different temperatures and with the movement in different positions.

Poising a balance by observing its errors on a timing machine while the watch is running at a reduced amplitude and at various positions.

French term for a movement blank, i.e. an incomplete watch movement which is sold as a set of loose parts, comprising the main plate, the bridges, the train, the winding and setting mechanism and the regulator. The timing system, the escapement and the mainspring, however, are NOT parts of the “ébauche”.

A nickel, steel alloy containing other additions such as chromium, manganese, titanium, tungsten or beryllium, which has a very low thermoelastic coefficient over the range of temperatures commonly encountered by a watch. Used in modern balances and springs, derived from the words “elasticity” and “invariable”.

Provides the balance with fresh additions of energy at regular intervals, and simultaneously prevents the movement from racing ahead and expending all its energy in a few mad seconds.