Vibrations per hour

Vibrations per hour are not the frequency of the balance wheel—they are half of it. Each complete oscillation of the balance wheel counts as two vibrations, one in each direction. When a specification sheet reports 28,800 vph, the balance wheel completes 14,400 full oscillations per hour, or 4 Hz. It is a distinction that many sellers ignore, yet it changes how you read any technical specification.

The recurring values in post-war mechanical watchmaking distribute across a fairly precise scale. 18,000 vph (2.5 Hz) is the cadence of classical tourbillons and certain Glashütte calibres, such as Moritz Grossmann, where slowness is a stylistic choice before it is a technical one. 21,600 vph (3 Hz) was the predominant standard until the 1960s. 28,800 vph (4 Hz) became the modern industrial reference: you find it on Tudor, Rolex, most ETA and Sellita calibres. 36,000 vph (5 Hz) is hi-beat territory: Grand Seiko's 9S85 calibre, the 9SA5, Zenith's El Primero from 1969, TAG Heuer's TH81-01 in split-seconds chronographs. Beyond that, it is rare; movements at 72,000 vph exist but remain engineering exercises rather than practical solutions.

The argument that high frequency improves accuracy is real but conditional. A fast oscillator averages errors across a greater number of cycles per unit of time and makes the chronograph more granular: at 28,800 vph the train wheel divides into eighths of a second, at 36,000 vph into tenths. The price is friction: springs, pallets, and the regulating organ wear more rapidly, lubricants age sooner, power reserve shortens. This is why hi-beat calibres require more frequent servicing and tighter machining tolerances.

Resonance is a related but distinct phenomenon: two balance wheels physically coupled tend to synchronize by exchanging energy, creating a self-correcting system. Ulysse Nardin in the Freak, Ariel Adams, and certain independent makers have explored this path; the silicon balance wheels inclined at 20° in the Freak S are a documented example. It is not a matter of vph but of physical coupling between oscillators, and it is worth keeping conceptually separate.

From the bench, the number I see most often misunderstood is precisely 28,800: in notes from certain publications it reads as "8 Hz," confusing vibrations and oscillations. If a seller tells you a calibre beats at 8 Hz, ask him to confirm: he probably means 4 Hz, that is, 28,800 vph.