Mechanical watch movement frequency

Last Updated on November 16, 2024 by Jason

Frequency is a term that is used regularly in these pages when discussing the specifications of watch movements. Movement frequency in a mechanical watch refers to the number of oscillations or vibrations the balance wheel makes per hour. It’s typically measured in Hertz (Hz) or vibrations per hour (VPH) or beats per hour (BPH). For example, a modern watch with a frequency of 4 Hz oscillates 28,800 times per hour (4 Hz x 60 seconds x 60 minutes). In this post, we hope to define the concept of frequency in watchmaking, but first, we probably need to explain a few definitions.

What is an oscillation?

In watchmaking, an oscillation refers to the complete back-and-forth movement of the balance wheel in a mechanical watch. This movement is essential for controlling the timing of the watch, as it governs how quickly the gears move and, consequently, how fast the hands of the watch rotate. The balance wheel swings in one direction and then returns to its starting point, completing one full oscillation. An oscillation consists of two beats: one when the balance wheel swings in one direction and another when it swings back. For example, if a watch has a movement frequency of 28,800 beats per hour (VPH), that means it has 14,400 oscillations per hour (since each oscillation consists of two beats).

How Hertz relates to watch movements

In watchmaking, Hertz (Hz) is a unit of measurement used to express the frequency of oscillations in a mechanical watch, specifically how many times the balance wheel oscillates per second. One Hertz equals one complete oscillation (back-and-forth movement) per second. For example, a watch with a movement frequency of 4 Hz means that the balance wheel oscillates 4 times per second, resulting in 8 beats per second (since each oscillation has two beats).

Certina Waterking, with a movement frequency of 19800 vph.

To convert a watch’s movement frequency from vibrations per hour (VPH) to Hertz (Hz), the following formula is used:

This formula works because each oscillation is equivalent to 2 beats, and there are 3600 seconds in an hour.

For a watch movement, like the Certina Waterking above, with a frequency of 19,800 VPH:

Importance of movement frequency in watchmaking

Frequency in watchmaking is important for a number of reasons, which are explained below:

Accuracy

A higher movement frequency generally improves the accuracy of a watch because the balance wheel makes more frequent adjustments, reducing the impact of minor external influences, such as wrist movements or positional changes. Watches with higher frequencies can make finer time corrections, which is why high-beat watches tend to be more precise.

Smoothness of the second hand

The sweep of the second hand is noticeably smoother in watches with higher frequencies because each beat occurs in shorter intervals. In contrast, a low-beat movement may produce a visible “tick” each time the second hand moves, while a high-beat movement creates a smoother, almost continuous motion.

Wear and tear

Higher frequency movements tend to wear out parts faster due to increased friction and energy consumption. As a result, watchmakers must use more durable materials or apply advanced lubrication to ensure longevity. On the other hand, lower-frequency movements experience less stress on their components, making them more durable and often preferred in watches designed for longevity.

L633.1 (ETA 2824-2) movement with a 28,800 vph frequency.

Power Reserve

Higher frequency movements typically consume more power, which reduces the watch’s power reserve—the length of time a fully wound watch can run without additional winding. Watchmakers must carefully balance movement frequency with power efficiency to optimize the performance of the watch.

Vintage vs. modern innovation

Traditional watches often operated at lower frequencies, such as 18,000 VPH, whereas modern innovations have pushed frequencies higher for increased precision. For example, the Zenith El Primero is famous for its high-beat movement at 36,000 VPH, allowing it to measure time to the nearest tenth of a second.

Roamer MST 371 movement. — Roamer MST 371 movement, 18,000 VPH.

Common movement frequencies

18,000 vph (2.5 Hz): Historically common in vintage watches.

21,600 vph (3 Hz): Common in older watches or slower-beat modern watches.

28,800 vph (4 Hz): The most common modern mechanical movement frequency.

36,000 vph (5 Hz): Found in high-frequency watches designed for better precision.

Summary

The movement frequency of a mechanical watch is a key factor in determining a watch’s precision, smoothness, durability, and power reserve. Watchmakers carefully balance frequency with the design and purpose of the watch, choosing the best compromise between accuracy and durability.