Vibrations per hour are not the balance wheel frequency: they are half of it. Every complete oscillation of the balance wheel counts as two vibrations, one in each direction. When a technical sheet reports 28,800 vph, the balance wheel completes 14,400 full oscillations per hour, or 4 Hz. It's a distinction that many sellers ignore but which changes how you read any technical specification.
The recurring values in post-war mechanical watchmaking are distributed on a fairly precise scale. 18,000 vph (2.5 Hz) is the rate of classical tourbillons and certain Glashütte calibers, like Moritz Grossmann, where slowness is a stylistic choice before it's a technical one. 21,600 vph (3 Hz) was the predominant standard until the Sixties. 28,800 vph (4 Hz) became the modern industrial reference: you find it on Tudor, Rolex, most ETA and Sellita calibers. 36,000 vph (5 Hz) is hi-beat territory: Grand Seiko's 9S85 caliber, the 9SA5, Zenith's El Primero from 1969, TAG Heuer's TH81-01 in split-seconds chronographs. You rarely go beyond; 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 over 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 out more quickly, lubricants age faster, the power reserve shortens. This is why hi-beat calibers require more frequent servicing and tighter manufacturing tolerances.
Resonance is a related but distinct phenomenon: two physically coupled balance wheels tend to synchronize by exchanging energy, creating a self-correcting system. Ulysse Nardin in the Freak, Ariel Adams and some independent watchmakers have explored this path; the silicon balance wheels tilted 20° in the Freak S are a documented example. It's not a matter of vph but of physical coupling between oscillators, and it's worth keeping conceptually separate.
From the bench, the number I see most often misunderstood is exactly 28,800: in some magazine notes you read it as "8 Hz," confusing vibrations and oscillations. If a seller tells you a caliber beats at 8 Hz, ask for confirmation: they probably mean 4 Hz, that is 28,800 vph.