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What Is Movement Frequency and Why Is It Important in Watchmaking?

Grand Seiko Hi-Beat Caseback

We throw around a lot of different horological numbers and watch specifications; it’s kind of our thing: case sizes, complications, and all the good stuff in life. But there’s one number we’ll often gloss over that perhaps we shouldn’t, a number that’s every bit as fundamental to the chronometric performance of a timepiece as its hands. I’m of course talking watches and movement frequency.

What is frequency in a watch movement?

If you’ve ever glanced at the specs of a watch and seen some absurd number rendered in vph/bph (vibrations per hour/beats per hour) or a much smaller number in the same space displayed in Hz (Hertz), that’s a watch’s frequency. But what does that actually mean and, more importantly, why does it matter?

Christiaan Huygens 1675 Balance Spring Diagram

The original drawing by Christiaan Huygens who invented the balance spring in 1675.

Stop me if this is a bit too basic (and by that, I mean skip a couple of paragraphs), but at the centre of every watch is an oscillator; its beating heart, if we’re to take the usual, overly played-out metaphor. An oscillator is just a bit that moves backwards and forwards at a hopefully constant rate. In most watches, this is the balance spring that coils and uncoils over and over again. In a quartz watch, it’s the crystal that vibrates as the electrical current passes through. Both serve the exact same function, to different degrees.

A movement’s frequency therefore is the speed that this oscillator moves back and forth every hour. If you flip over your watch – provided you have an exhibition caseback – you should be able to see the balance spring moving. Count how many times it coils or uncoils, times that by 60 and you have its frequency. Simple.

Omega Silicon Si14 Balance Spring

In 2008 OMEGA released the Si14 balance spring to resist magnetic forces, reduce deviation and improve chronometric stability.

I prefer to articulate frequency in beats per hour (bph), largely because of that aforementioned heart metaphor, but also because it just sounds a bit more accessible than the alternative vibrations per hour (vph). You may also see it expressed in the more technical Hz or Hertz, which is the number of complete oscillations (a combined back and forwards) that the balance makes. If bph is the number of ‘ticks’, Hz is the number of ‘tick-tocks’. To get it, divide the bph by 60 for the number of movements per minute, then 60 again for the number per seconds, then halve it again for Hertz. It’s all relatively straightforward as horological maths goes.

Why does frequency matter?

Girard-Perregaux Neo Constant Escapement Balance Spring

Girard-Perregaux’s Neo Constant Escapement Balance Spring

So why does this matter? It obviously does, or I wouldn’t be devoting these pages to it. Well, as it’s converting raw energy into regular motion, frequency comes down to the kinetic representation of time. The mainspring in the barrel that gets wound transfers energy to the balance spring, which oscillates to lock and unlock the escapement, allowing the energy to regularly flow into the rest of the watch with its gear train, hands and other indicators. The more that happens, the smaller the units you’re dividing time into and the more precise your watch.

At least, that’s the basic reason. Faster movements also have the added benefit of being more resilient to outside forces. If a slow-beating balance gets momentarily knocked off-kilter and misses a beat that means a lot more than if a fast-beating balance does the same. It means that when it comes to pure chronometric performance, you want a higher frequency. So why then are there plenty of high-end watchmakers out there that opt specifically for slower bphs?

Garrick S2 Deadbeat Seconds MK2 Engine Turned Anchor Hands with 18,000 vph/bph (2.5 Hz) frequency

Garrick S2 Deadbeat Seconds MK2 with 18,000 vph/bph (2.5 Hz)

Well, higher frequencies tend to mean smaller balance springs, lower frequencies mean larger. That makes sense; it takes less time for a tiny spring to coil and uncoil than a large one. The problem however is twofold. On the chronometric side, faster frequencies require more energy from the mainspring and thus drain your power reserve a lot quicker. The difference in energy consumption between a watch that beats 36,000 times and hour and one that beats 21,600 or less is obviously going to be massive.

Then there’s the indisputable fact that larger balance springs are just nicer to look at. Brands like Kari Voutilainen or Garrick make oversized balances actual features of their watches and they’re glorious to behold. On the other hand, there’s something frantic and panicky about a Grand Seiko Hi-Beat. Then there was Zenith’s LAB Defy with its full movement-width oscillator, which gave me conniptions. A novel, innovative creation for sure, but one that sounds like a case full of bees.

How much does frequency matter?

Zenith calibre El Primero 3600 Watch with 3,600 vph/bph (5 Hz) frequency

Zenith Defy Skyline Chronograph with 3600 vph/bph (5 Hz)

This last question is the tricky part, because while frequency is integral to the running of a watch, it’s not the only thing that is. Except in very rare circumstances – watches with constant force mechanisms for example – accuracy goes down as the balance is fed less power. This is called isochronism and is why even automatic watches should be wound when you put them on if they have any hope of keeping good time. Then there’s the fact that the position and orientation of the watch on your wrist can have an impact on its performance too.

These are both things that a talented watchmaker can take into account and compensate for, regulating the movement in different positions and utilising other methods (such as that aforementioned constant force mechanism) to account for isochronism. Even when using a slower beating movement, these calibres can be more accurate than a high-frequency number with less attention lavished on it. In most instances, frequency is something that can be compensated for.

Zenith calibre El Primero 3600 with 3,600 vph/bph (5 Hz) frequency

Zenith calibre El Primero 3600 with 3,600 vph/bph (5 Hz)

The elephant in the room is that until now we’ve been discussing time-only watches. The one thing that a high-frequency movement is vital for however is the chronograph. In everyday life a tenth of a second doesn’t matter, but when you’re timing a race, it’s everything. And where the minute division of time in most watches just leads to a smoother second hand, in brands like Zenith or TAG Heuer, it’s created some phenomenally accurate stopwatches that can measure down to 1/100th of a second. In most watches the frequency is a useful spec; in chronographs it’s downright definitive.

Omega Co-Axial 3861

Omega calibre 3861 with 21,600 vph/bph (3 Hz) frequency

Otherwise, it all really comes down to what specific watchmakers want to achieve. Grand Seiko, the poster child for high frequency movements with their superb Hi-Beat collection, is after every day accuracy and a smooth second hand; Tissot on the other hand use the Powermatic 80, a calibre that ETA specifically developed at a lower frequency, 21,600 vph/bph (3 Hz) to be precise.

TAG Heuer Mikrotimer Chronograph with 3.6 million vph/bph (500 Hz) frequency

TAG Heuer Mikrotimer Chronograph with 3.6 million vph/bph (500 Hz)

Omega landed somewhere between, determining after years of testing that the perfect frequency for their George Daniels-design Co-Axial escapement is 25,200 vph/bph (3.5 Hz). TAG Heuer’s Mikrotimer chronograph was specifically designed to time 1/1000th of a second. It’s frequency? 3,600,000 vph/bph (500 Hz).

So, in short, frequency matters and is integral to how you approach the design of a watch. But it’s one factor among many and choosing your timepiece according to how often it beats would be like choosing a watch for its power reserve and nothing else, which you should never do – if only because with a frequency of 32,768 beats per second, that would invariably lead you to quartz.

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About the author

Sam Kessler

Legend has it that Sam’s first word was ‘escapement’ and, while he might have started that legend himself, he’s been in the watch world long enough that it makes little difference. As the editor of Oracle Time, he’s our leading man for all things horological – even if he does love yellow dials to a worrying degree. Owns a Pogue; doesn’t own an Oyster Perpetual. Yet.