Why Mechanical Watches Run Slow

Quick Questions

Why does my automatic watch lose time every day?
Is a 20-second daily loss normal for a mechanical watch?
How does a lack of wrist movement affect watch accuracy?
Can cold weather make a mechanical watch run slow?
What should I do if my watch stops after being magnetized?

To grasp why a mechanical watch loses time, you must first understand that error is cumulative. For instance, if your watch runs slow by 20 seconds per day, you won't notice the difference in a single day, but after half a month, it will be about 5 minutes slow, and after a month, a full 10 minutes. This accumulation often creates the illusion that the watch is progressively slowing down. The industry standard for acceptable accuracy is within ±30 seconds per day.

Common Causes of Slow Mechanical Watches

1. Insufficient Mainspring Power
Most self-winding watches need at least 8 hours of daily wear to keep the mainspring fully energized. If your daily activity is minimal, the watch doesn't get enough winding, leading to a slow pace or even intermittent stopping.

2. Dirt and Thickened Lubricants
Over time, or due to poor case sealing, the movement can accumulate dust and grime, causing the lubricants to thicken. This increases friction and slows down the watch. A professional servicing usually resolves this issue.

3. Cold Weather Effects
Low temperatures can cause lubricants to congeal, increasing resistance. The solution is to clean the movement and replace the oil with a type that remains fluid in cold conditions.

4. Stops and Starts Due to Impact
If your watch has been dropped or knocked, internal parts may shift or sustain minor damage, leading to erratic stopping and starting. This can also involve a slightly bent balance staff or a tangled hairspring, causing the balance wheel to oscillate briefly then stop.

5. Water Ingress Not Properly Treated
Some enthusiasts try DIY methods like sun-drying, using a hairdryer, baking, or placing the watch with desiccants. These methods are ineffective because they can't remove moisture trapped deep inside the movement, and they may even cause additional damage. The only proper solution is a full disassembly, cleaning, and re-oiling to prevent rust and corrosion of metal parts.

6. Exposure to Magnetic Fields
Mechanical watches are highly sensitive to magnetism. Prolonged contact with electronic devices can magnetize the watch, causing it to run fast, slow, or even stop. Demagnetization is required to restore normal operation.

In summary, a slow-running mechanical watch is often a symptom of external factors or maintenance issues, not necessarily a broken watch. Ensure you wear it enough to maintain power, and if problems persist, consult a professional watchmaker for a proper diagnosis and solution.