Mechanical Watch Accuracy: Understanding

Quick Questions

What is an acceptable daily error for an automatic mechanical watch?
Are mechanical watches inherently less accurate than quartz watches?
How do magnetic fields affect mechanical watch timekeeping?
Why does my mechanical watch gain or lose time depending on position?
Can regular maintenance improve the accuracy of my automatic watch?

When it comes to timekeeping, mechanical watches and quartz watches operate on entirely different principles. Quartz movements rely on the piezoelectric properties of a quartz crystal to maintain a stable frequency, which ensures high accuracy. In contrast, mechanical watches are powered by a mainspring and regulated by a balance wheel, a system that is inherently susceptible to various external factors. Consequently, mechanical watches exhibit a daily rate error that is larger than quartz, but this is a characteristic feature rather than a flaw.

What Is the Standard Daily Rate Error for Automatic Mechanical Watches?

According to industry norms, a standard automatic mechanical watch should run within a daily error range of ±30 seconds. However, if the movement has received chronometer certification—such as from the COSC (Contrôle Officiel Suisse des Chronomètres)—the acceptable deviation is tighter, typically between -4 and +6 seconds per day. This certification denotes a higher level of precision after rigorous testing under various conditions.

The power source of an automatic watch is the wearer's arm movement, which causes the oscillating weight to rotate and wind the mainspring. On a full wind, a typical mechanical watch can run for about 36 hours, but under normal daily wear, it may only operate for around 16 hours before needing additional winding. If the watch is left stationary for an extended period or the wearer is sedentary, the power reserve can be depleted, causing the watch to stop.

Error Tolerance by Grade

In the watch industry, mechanical watches are classified according to their timekeeping accuracy. For men's self-winding watches, a daily error between -30 and +45 seconds is considered excellent, while -45 to +60 seconds is deemed first-class, and -60 to +75 seconds is acceptable as a standard grade. These classifications provide a benchmark for consumers to assess the performance of their timepieces.

To minimize these errors, many watchmakers incorporate a flywheel mechanism into the movement. This device helps to stabilize the oscillation, reducing the impact of external disturbances. Brands like Longines and some domestic manufacturers utilize this technology to enhance accuracy.

How to Prevent Your Mechanical Watch from Losing Accuracy

Mechanical watches are subject to various influences that can alter their timekeeping. These include the gradual loosening or tightening of the mainspring, the condition of the movement's lubrication, changes in temperature, and exposure to magnetic fields. These factors can lead to an imbalance in the mechanical transmission, resulting in timekeeping errors. It is important to note that even a perfectly adjusted watch will not maintain its accuracy indefinitely; the rate may drift over time.

Power Management: To ensure your automatic watch runs within its normal range, it is essential to provide adequate winding. A full wind typically requires about 25 to 30 turns of the crown. If the watch is not worn daily, it may stop due to lack of power, so manual winding is necessary.
Consistent Wear or Use a Watch Winder: For those who own multiple mechanical watches, it is advisable to use a watch winder to keep the movements active. Long periods of inactivity can cause the lubricants to settle, which may affect accuracy.
Proper Care and Handling: Avoid subjecting your watch to strong shocks or magnetic fields. Parts of the movement are made of steel, which can become magnetized, causing the balance wheel to oscillate irregularly and the watch to run fast. Keep it away from appliances like refrigerators, speakers, and magnetic clasps.

Common Causes of Timekeeping Errors

Magnetic Influence: When a mechanical watch is exposed to a magnetic field, the hairspring may become magnetized, causing the watch to gain time. Even a single exposure can affect accuracy.
Power Reserve Depletion: If you do not wear the watch regularly or your wrist movement is limited, the mainspring may not be wound sufficiently. This can lead to the watch running slow or stopping, especially if the power reserve is low.
Improper Handling: Sudden impacts or vigorous wrist movements can cause the hairspring to tangle or the shock absorber to dislodge. This can result in the watch running fast or even stopping. Additionally, wearing a watch in water when it is not adequately water-resistant can damage the movement.
Lack of Maintenance: As a precision instrument, a mechanical watch requires regular servicing. Over time, the movement's oils can dry out or become contaminated, and screws may loosen. Without proper maintenance, accuracy will deteriorate, and the watch's lifespan may be shortened.

Can You Adjust the Accuracy of a Mechanical Watch?

The daily error of a mechanical watch can often be adjusted, but it requires the expertise of a skilled watchmaker. The specific adjustment method depends on the movement's design. Some movements have a regulator that can be moved to speed up or slow down the watch, while others may require more intricate procedures. It is not a task for the average wearer to attempt, as it involves opening the case and manipulating delicate components.

For those who wish to check their watch's accuracy at home, there are simple methods. You can compare the time with a reliable reference over 24 hours, noting the gain or loss. However, for a precise assessment, a professional timegrapher is recommended.

When to Adjust Your Watch's Time

If your watch has a date complication, it is advisable to adjust it during the day, avoiding the period between 10 PM and 2 AM (or 8 PM and 4 AM for some movements). Adjusting during this window can interfere with the date change mechanism, potentially causing damage or incorrect date display.

When setting the time, pull the crown out to the time-setting position and turn it clockwise. Avoid setting the time counterclockwise, as this can put unnecessary stress on the movement and may affect accuracy.