Amplitude

The clearest definition found for this entry is in a granted patent rather than a standard. European patent EP 2 917 787 B1, held by Patek Philippe SA Geneve and published on 19 August 2020, speaks of "l'amplitude d'oscillation du balancier exprimee en degres par rapport a la position d'equilibre": the amplitude of oscillation of the balance, expressed in degrees with respect to the equilibrium position. The same patent compares a movement's behaviour at "amplitude d'oscillation de 150°" and at "amplitude d'oscillation de 300°", and records that "la marche diminue progressivement au fur et a mesure que l'amplitude d'oscillation diminue": the rate falls progressively as the amplitude falls.

Amplitude is read because it changes, and because a change in it shows up as a change in rate. French patent publication FR 2 767 205 A1, an optical and acoustic method of measuring balance amplitude filed in 1997 by Femto, states that an amplitude that is too small or too strong "may, in fact, affect the accuracy of the watch when it is in a vertical position", while fluctuations in amplitude over time may show "defects in the gear train or the spring barrel". The quantity is therefore used as a diagnostic alongside daily rate, not instead of it.

What is open: no standards body's definition of amplitude has been read. FH's list of available NIHS standards, valid from April 2026, includes one on horological vocabulary ("NIHS_02-03_fr: Vocabulaire horloger - Partie 1: Definitions technico-scientifiques", 1982), but the list gives titles and years only, not the text of the norms, and no standard in it is titled for amplitude. The definition above is quoted from a manufacturer's granted patent, a primary document, but not a normative definition issued by a standards body or metrology institute.