mechanical watch movement also has a heartbeat; the steady ticktock of the escapement. This is the essential mechanism that regulates the release of energy from the mainspring, transforming it into controlled “ticks” and “tocks.” And even though escapements are roughly the same size, their heartbeats, or rather frequencies, range widely from slow to fast. Why is that, and what effect does the frequency have on the accuracy of the movement, its longevity and its power reserve?

Let’s first talk extremes. Although not wearable on the wrist, there’s a mechanical clock deep inside a mountain in West Texas, USA, that needs mentioning. The Clock of the Long Now is currently being constructed on private land owned by Amazon founder Jeff Bezos. He’s funding the project, and once completed, the clock will produce a deep-sounding ticktock once a year (!). The gigantic timepiece, also known as the 10,000-Year clock, is designed to keep time for 10,000 years and serves as a symbol of long-term thinking. It is being built by the Long Now Foundation, and smaller prototypes are on display at the Science Museum in London, UK, and at The Long Now Museum & Store at the Fort Mason Center in San Francisco.

To put one annual beat in perspective, a breakdown is necessary. The 10,000-year clock’s escapement beats with two vibrations per year. Now, a pocket watch movement usually beats at 18,000 vibrations per hour (vph). A single oscillation sees the balance move in one direction, giving you the “tick”, then the other for the “tock”. At 18,000 vph, this means that the seconds hand makes five jumps per second. 18,000 vph corresponds to 2.5 hertz, with 1 hertz (Hz) being the International System of Units (SI) unit of frequency, defined as one cycle or periodic event per second. When a movement makes two vibrations per year, what is the frequency measured in hertz? This calls for mathematics. When you divide one annual cycle by 31,536,000 seconds, you get approximately 3.17 × 10-8, which corresponds to about 31.7 nanohertz, and that’s an (almost) impossible-to-grasp beat rate.

Two slow beats a second

What’s good to know is that for a stationary object like a clock, a strong inertia is preferred for good accuracy; therefore, a low frequency is also preferred. For a constantly moving wristwatch, a higher frequency is better suited to reach good accuracy. That’s why the slowest beating movement inside a wristwatch beats much faster than the 10,000-year clock. The Antoine Martin Slow Runner is regarded as the slowest-beating mechanical wristwatch ever produced. It features a very large 24mm balance wheel oscillating at just 1 Hz, or 7,200 vph. This translates to one ticktock each second, meaning the balance wheel swings once in each direction every second, and the movement advances the seconds hand twice per second. A low-frequency regulator, like the one in the Slow Runner, can negatively affect accuracy.

The most common frequency in watchmaking today is 28,800 vph (4 Hz, or 8 beats per second). The reason behind that is that a 4 Hz movement offers the optimal balance between accuracy, durability and power reserve. When a movement has a higher beat rate, it is likely to be more accurate than the AM36.001 calibre inside the Antoine Martin Slow Runner, but the long 92-96 hours of power reserve is hard to beat for a 4 Hz movement. Watchmaker Martin Braun, the man behind Antoine Martin, also built the Slow Runner to prove its capability to reliably keep time. A slower beat means less wear and tear on movement components, resulting in fewer service intervals.

Picking up fast vibrations

The 2012 TAG Heuer Carrera Mikrogirder is the exact opposite of the Antoine Martin Slow Runner. This prototype chronograph has a beat rate of 1000 Hz. The Mikrogirder, a concept watch designed to showcase TAG Heuer’s R&D capabilities in high-frequency, precision timing, is the final watch in a line of high-beat chronographs that began with the Mikrograph 100 (50 Hz) and the Mikrotimer 1000 (500 Hz), both of which use conventional balances with lever escapements. To reach 1000 Hz, a linear oscillator, not a spiral shape balance spring, vibrates isochronously at a very small angle, resulting in a mind-blowing oscillation frequency of 7.2 million vibrations per hour. This has the chronograph’s seconds hand race around the dial 20 times per second, allowing measurement to a two-thousandth of a second.

As with mammals, the larger the movement’s balance wheel (heart), the slower the beat rate (heartbeat). Also, the higher the frequency, the lower the power reserve. When a movement has a beat rate of 7.2 million vibrations per hour, it quickly runs out of energy. A comparison to mammals comes in handy again. For example, the aforementioned mouse’s heart beats more than 600 times per minute, exhausting its “allotment” within just two to three years. The blue whale’s 5 heartbeats per minute stretch its lifespan to up to 90 years. And it’s not just a question of energy. Higher beat rates place greater strain on the mechanism, whether it’s a heart, which is, in essence, a pump, or an escapement. Already at 36,000 vph, lubrication, particularly between the pallets and the escape wheel, can become problematic. This is why silicon is preferred for high-beat movements. Non-alloy silicon surfaces, particularly when oxidized, are extremely smooth and hard, reducing friction to a point where oil is unnecessary. 

Time to choose a beat

The fastest-beating mechanical watch in current, non-concept production is the Zenith Defy 21, which uses the El Primero 9004 calibre. This movement features a chronograph with its own escapement, vibrating at 360,000 vph (50 Hz). This rapid rate allows measuring time to 1/100th of a second, with the centre chronograph hand completing one full rotation per second. The timekeeping part of the calibre beats at 36,000 (5 Hz), a choice showing accuracy was the main objective when creating the movement.

Matters of the heart in relation to mechanical movements are all about priorities and preferences. A slow beat allows for a long power reserve and less maintenance. When accuracy is of the utmost importance, a faster ticktock is preferred. The watchmaker chooses the beat that best suits its purpose. To find out what that purpose is, just listen to the speed of the ticktock; it says it all.