Even from a distance, it’s usually pretty easy to tell quartz watches and mechanical watches apart. All you have to do is check whether the second hand jumps forward once per second or has a more smooth, constant movement. You probably already know this, but for those who don’t: How the second hand ticks is directly related to the watch’s balance frequency. However, there are many myths and rumors surrounding the frequency of a watch. Is it true that high-frequency timepieces – also known as “high-beat” watches– are more precise than low-frequency models? Why are there watches with two different escapements and different frequencies like the Zenith 21 Defy? And why does the frequency of a chronograph movement have an influence on dial design? This article has all the answers. We’ll explain the advantages and disadvantages of each movement type, while also clearing up the most common rumors.
Higher Frequency = More Accurate?
Improved accuracy is the feature associated with high-frequency movements. Some prominent examples are the aptly-names Grand Seiko Hi-Beat models. While watches usually tick at 3 or 4 Hz, Grand Seiko’s 9S family of movements offer a frequency of 5 Hz. Zenith‘s historic El Primero is another famous example of this type of “speed demon.” The Hz value represents the number of oscillations per second. However, it’s more common to indicate the number of alternations per hour: e.g., 21,600 (3 Hz), 28,800 (4 Hz), and 36,000 (5 Hz). Why go by alterations instead of complete oscillations? It’s simple: The balance wheel triggers the lever on its way forward and as it swings back. Both trigger the gear train so that the balance wheel receives an impulse – a little push – from the lever. So at a frequency of 3 Hz, three full oscillations, the second hand jumps six little steps and six audible ticks can be heard per second. Per hour, that’s 21,600 ticks. That’s why the number of alternations is useful.
But let’s get back to accuracy. Interestingly, the accuracy of high-frequency watches is often justified by comparing them to quartz watches. Most quartz timepieces have a balance frequency of 32,768 Hz, a value no mechanical watch could ever hope to achieve. It’s easy to assume the this higher frequency leads to a more accurate watch. While that’s not wrong, the real connection is much more complex.
What really makes high-beat watches more precise?
For comparison’s sake, let’s look at precision pendulum clocks like the ones from Siegmund Riefler. These timekeepers were known for their legendary precision and were used in observatories and for scientific purposes around the globe. With a frequency of 0.5 Hz, or one alternation per second, these pendulum clocks were accurate to within +/- one-hundredth of a second per day. This shows that accuracy doesn’t solely depend on the frequency of the pendulum or the balance wheel. Instead, it’s much more about keeping a constant frequency – under all conditions and over the timepieces’ entire service life. Many factors come into play here, such as temperature, impacts, fluctuations in power, and wear and tear. A wristwatch will experience much more vibration than a grandfather clock in an air-conditioned room. In addition, the power regulator, balance wheel, and balance spring must be able to function consistently regardless of their orientation. The real challenge of the regulator is, thus, to maintain consistent oscillation under all conceivable circumstances. Once you understand how this is related to frequency, you can appreciate the bigger picture.
One way to ensure consistent frequency is found in the differences between high and low-frequency oscillation systems and, most importantly, how they respond to impacts. This is where high-frequency movements can implement one of their deciding advantages. They recover much faster from impacts in that it takes less time to return to the desired frequency. They thus offer more stable frequencies. It follows then that a wristwatch, which is subjected to all kinds of accelerations and impacts, remains more precise when the balance wheel oscillates at a higher frequency.
If you could define the quality of an oscillation system in just one world, this would probably be the quality factor, or Q factor, a term used in both physics and watchmaking. This value shows the relation of the oscillator’s energy to the loss of energy due to friction per oscillation. Watchmakers try to keep the energy input as low as possible because interfering with the escapement, while necessary, is also the greatest disruption to the constant oscillation of the balance wheel. Increasing the frequency of an oscillating system is the most feasible way to achieve this and increase the quality factor. However, minimizing bearing friction and air resistance is also an important consideration. Jaeger-LeCoultre‘s Gyrolab movement in the Geophysic True Second even has a balance wheel that is optimized for aerodynamic performance. By the way, the quality factor is a unitless value, lying somewhere around 300 for common mechanical watches. For quartz oscillators, it’s generally a 5-digit number.
A third advantage of a high-frequency movement is its behavior when the balance wheel isn’t perfectly balanced. Higher frequencies serve to minimize the effect of gravity in such cases. Since a 100% perfect balance can never be achieved, this advantage is critical for the precision of high-beat watches.
The Problems with High-Beat Movements and How Manufacturers Have Solved Them
Bearing in mind the previous information, one might assume that high frequency of the escapement should be the highest goal in watchmaking. However, we have neglected some critical factors: the energy balance of the watch and its maintenance. While high-frequency escapements are very precise, they consume energy at a higher rate. In a high-beat watch, the lever and escape wheel have more contact with each other than in a low-beat watch. This means faster wear and tear, shorter power reserves, and more frequent maintenance – and these are not at all in line with consumer demands for less hassle and longer intervals between services. High-beat movements often require special lubricants, and there is a risk that oil from the intended components could be shaken off due to the high speeds. The escape wheel also has to meet higher demands. It must have very low inertia so that it can accelerate with the desired frequency and then also be able to come to a stop again. The escape wheel of Grand Seiko Hi-Beat movements has a complex structure with clearly recognizable cutouts. The modern Chronergy escapement from Rolex exhibits a similar inertia-reducing geometry.
Balance wheels that oscillate at high frequencies tend to be rather small. This makes it difficult to manually regulate them. Compared to more leisurely oscillating screw balances like those found in A. Lange und Söhne watches, these movements seem rather hectic. Slowly oscillating balance wheels are favored by traditional manufacturers and independent watchmakers for their longer power reserves, easier regulation, and, of course, the imposing sight of a large and slow balance wheel. An extreme example of this category is the Antoine Martin Slow Runner. Its 1 Hz balance wheel is almost as wide as the movement itself.
What Frequency Means in Chronographs: A Special Case
In chronographs, the frequency of the escapement is responsible for another important characteristic, which often leads to confusion about the definition of “precision” in timepieces with this complication. When it comes to precision in chronographs, the same applies as what has been discussed previously.
However, there is a catch: Because the second hand (or stop seconds hand) only moves forward in discrete steps, it can only display a measured interval with a certain degree of accuracy. A watch that ticks at 3 Hz allows is accurate to within one-sixth of a second. Accordingly, the Zenith El Primero with a frequency of 5 Hz allows the measurement of tenths of a second. No matter how precise a chronograph like that is, it won’t be able to measure hundredths of a second because the hand simply doesn’t stop at that many positions per second. In order to measure hundredths of a second, one would need a 50 Hz escapement. Such a watch with a conventional escapement would have an impractically low power reserve.
But there’s a solution to this too: One can have two completely separate movements with independent escapements in the same watch. This was achieved a few years ago in the discontinued TAG Heuer Mikrograph, and the technology celebrated its comeback through the LVMH-owned brand Zenith with their Defy 21. This watch tells time through a 5 Hz movement with a 50 hour power reserve, while the chronograph function is made possible by an independent movement that only runs for 50 minutes when fully wound, but it has an incredible balance wheel frequency of 50 Hz. The hand thus changes position an unbelievable 100 times per second. For readability, that hand goes all the way around the dial once every second, and a hudredths scale allows the wearer to read the exact interval measured.