What is Amplitude?

Amplitude is one of the most important measurements used to assess the performance and overall health of a mechanical watch movement. It refers to the angle of rotation of the balance wheel as it oscillates back and forth, typically expressed in degrees. For watchmakers, amplitude provides a direct window into how efficiently the movement is functioning, how well energy is being transmitted through the gear train and whether the watch requires servicing or adjustment.

Although amplitude is invisible to the wearer, it is fundamental to accurate timekeeping. A movement running with strong, stable amplitude is generally healthy, clean and well lubricated. One with low or irregular amplitude often signals friction, wear, contamination or other underlying issues. Understanding amplitude helps explain how a mechanical watch maintains precision and why servicing is essential to its longevity.

What Amplitude Measures

The balance wheel in a mechanical watch swings back and forth in a regulated motion driven by the escapement. Amplitude measures how far the wheel rotates from its resting point during each oscillation. This is recorded in degrees, with modern watches typically running between 270 and 310 degrees in a horizontal position when fully wound.

Amplitude is not a measurement of speed, but of distance travelled by the balance wheel. A higher amplitude indicates that the balance wheel is receiving adequate energy from the mainspring and encountering minimal resistance. Lower amplitude suggests energy loss, often due to friction or degraded lubrication.

The amplitude of a watch varies naturally depending on its position, level of wind and age of lubrication. However, excessive deviation from expected values provides valuable diagnostic information to a watchmaker.

The Role of Amplitude in Timekeeping

Amplitude affects the precision of a watch because it is closely tied to the balance wheel’s oscillation consistency. Ideally, the balance oscillates in a stable, symmetrical pattern. When amplitude drops too low, the balance wheel covers less distance, altering the duration of each oscillation and causing rate deviation.

Conversely, amplitude that is too high can lead to a condition known as knocking or rebanking, where the balance wheel rotates so far that it hits the banking pins or reaches the limits of the escapement. This disrupts the smooth locking and unlocking of the escapement teeth, resulting in severe timekeeping errors.

Maintaining amplitude within an optimal range is therefore essential. It ensures that the movement’s energy transmission is balanced, the escapement functions correctly and the watch keeps time reliably.

How Amplitude Is Measured

Amplitude is measured using a timing machine, also known as a watch analyser. This device listens to the sound of the escapement and calculates amplitude, rate deviation, beat error and other performance metrics. The watch is tested in multiple positions, such as dial up, dial down, crown up, crown left and crown right, to simulate real wearing conditions.

During measurement, the timing machine displays the amplitude in degrees. A watchmaker interprets these readings alongside other diagnostic information to determine whether the movement is performing within expected tolerances.

Consistent amplitude across positions is desirable, although some variation is normal. Large discrepancies may indicate positional friction, worn pivots, balance staff damage or uneven lubrication.

Expected Amplitude Values

Acceptable amplitude values vary depending on the type of movement, its age, design and condition. However, general guidelines help evaluate performance.

Typical values include:

New or freshly serviced modern movements: 270 to 310 degrees.
Older or vintage movements: 250 to 280 degrees.
Minimum acceptable amplitude for reliable accuracy: around 220 degrees.
Amplitude above 320 degrees: may risk knocking or excessive escapement contact.

These ranges are not absolute rules. High beat movements, for example, may display slightly different amplitude characteristics. Similarly, complications such as chronographs introduce additional energy demands that can affect amplitude readings.

Factors That Influence Amplitude

Amplitude is affected by numerous mechanical factors, many of which relate to energy transmission and friction. Understanding these influences helps diagnose issues when amplitude readings decline.

Common factors include:

Level of mainspring wind, as amplitude decreases naturally as the power reserve diminishes.
Condition of lubrication, since old or dried oils increase friction within the gear train and escapement.
Wear or dirt on pivots, jewels and gear teeth.
Balance spring condition, including contamination, magnetisation or distortion.
Escapement health, such as worn pallet stones or escape wheel teeth.
External shock or impact that may affect the balance staff or pivots.

Amplitude does not decline randomly. It is almost always the result of resistance somewhere within the movement.

Amplitude Across Different Positions

A watch’s amplitude varies depending on its orientation. Horizontal positions, such as dial up or dial down, generally produce higher amplitude because the balance staff pivots face less gravitational load. Vertical positions typically show lower amplitude due to increased friction on the pivots.

The difference between horizontal and vertical amplitude, known as amplitude delta, is an important diagnostic indicator. A healthy movement may show a delta of around 20 to 40 degrees. A larger delta can indicate wear, imbalance or lubrication problems.

Positional variance is a normal part of mechanical watch behaviour, but extreme differences warrant investigation.

Amplitude and Beat Error

Amplitude and beat error are separate measurements, yet they are closely related. Beat error refers to the symmetry of the balance wheel’s swing. If the wheel swings further in one direction than the other, the beat error increases.

Excessive beat error can indirectly affect amplitude by introducing inefficiency into the oscillation. A properly adjusted movement with minimal beat error tends to run with more stable amplitude, improving overall timekeeping.

A timing machine allows watchmakers to analyse both amplitude and beat error simultaneously, providing a more complete performance profile.

How Low Amplitude Affects a Watch

Low amplitude is one of the most common indicators that a mechanical watch requires servicing. When amplitude falls below expected levels, several issues may arise.

These include:

Reduced timekeeping accuracy, as the oscillation period becomes unstable.
Increased positional variance, causing the watch to run differently depending on wrist orientation.
More rapid sensitivity to shock or movement.
Potential for stoppage during low power reserve conditions.

Low amplitude does not always mean serious damage, but it does suggest that the movement is not operating efficiently. Routine maintenance can often restore proper performance.

Amplitude After Servicing

Following a full service, a properly cleaned and lubricated movement should show increased amplitude compared to its pre service readings. Watchmakers aim for stable amplitude across positions with minimal delta and sufficient safety margin below the knocking threshold.

Amplitude improvements are often one of the clearest signs that servicing was successful. The watch will keep time more reliably, require fewer adjustments and experience less wear over the long term.

Owners sometimes notice a watch running slightly fast immediately after servicing. This can occur because higher amplitude temporarily influences rate until the oils settle. A minor regulation after the break in period resolves this.

Amplitude in High Beat Movements

High beat movements, such as those oscillating at 36,000 vibrations per hour, present unique amplitude characteristics. Because the balance wheel oscillates more rapidly, the amplitude is typically slightly lower compared to standard 28,800 vph movements. This is not a flaw, but a natural consequence of the higher frequency design.

The increased frequency improves rate stability and compensates for reduced amplitude. Watchmakers evaluating high beat movements adjust their expectations accordingly, ensuring amplitude remains appropriate for the movement type.

Why Amplitude Matters to Collectors and Enthusiasts

Amplitude is not merely a technical detail for watchmakers. For collectors and enthusiasts, it provides reassurance that a watch is healthy internally. When purchasing a vintage watch, amplitude readings can reveal whether the movement has been neglected, improperly serviced or compromised by wear.

A strong, stable amplitude suggests that the movement is well preserved and capable of reliable performance. Conversely, low amplitude may reveal hidden issues that require attention. Understanding amplitude therefore empowers collectors to make informed decisions.

Conclusion

Amplitude is a foundational concept in mechanical watchmaking, reflecting how effectively a movement converts stored energy into precise, regular oscillation. It serves as a key diagnostic tool, a measure of mechanical health and a predictor of timekeeping reliability.

Although invisible to most wearers, amplitude shapes a watch’s performance every moment it is running. By understanding how amplitude works, what affects it and why it matters, one gains a deeper appreciation of the intricate balance of forces inside a mechanical watch. It is a reminder that accuracy depends not only on design, but on maintenance, condition and the delicate harmony of moving parts working in unison.