Chronometric tachometers and speedometers contain clock mechanisms with balance wheel movements. These movements are cleverly driven by the rotating input cable through a slipping clutch. A three lobe camshaft, whose rotation is driven by the clock, serves as a 'mechanical director'.

How does a Smiths Chronometric speedometer?

How did the Chronometric operate and why was it considered so accurate? This particularly neat and accurate design of speedometer uses the clock movement or chronometric principle, whereby speed indications are obtained at intervals of ¾ second, by means of an escapement mechanism.

What is Chronometric instrument?

The Chronometric speedometer / Tachometer is a principle commenced by the Jaeger speedometer company in Paris, France, in the 1920s and as such is a METRIC instrument, that is the dimensions, screws, threads etc are metric and not imperial as generally thought.