01Why a mechanical watch runs fast or slow
Every mechanical watch drifts a little. A balance wheel oscillating five or more times a second cannot keep perfect time the way a quartz crystal does, so a deviation of a few seconds a day is completely normal and well within factory tolerance for most movements.
The picture changes when the drift grows large. A watch that suddenly gains thirty seconds a day, or steadily loses a minute, is telling you that something specific has shifted inside it. These big deviations are not random; each one has a handful of likely culprits that a watchmaker would check in a predictable order.
The good news is that the direction of the error already narrows the field. Running fast and running slow point to different parts of the movement, so before you reach for any tool it helps to know which camp your watch falls into and what each one usually means.
02Running fast: the usual suspects
By far the most common reason a watch suddenly gains time is magnetism. When the hairspring coils become magnetised they stick together, the effective spring shortens, and the balance speeds up. The result can be tens of seconds or even several minutes a day, appearing overnight after the watch passes near a phone speaker, a tablet cover, a fridge magnet, or a laptop.
The other two causes are mechanical. Over-amplitude with knocking happens when the balance swings so far that the impulse pin slams past its safe arc, which can make the watch race; it often points to a service issue rather than a setting. And sometimes the watch is simply regulated a touch fast from the factory or a previous adjustment, producing a small, steady gain rather than a sudden one.
Always rule out magnetism before anything else. A demagnetizer costs around fifteen euros, takes seconds to use, and resolves the single most common cause of a watch running fast. There is no reason to suspect a service before you have demagnetised.
03Running slow: the usual suspects
Losing time usually comes down to the movement not delivering enough energy to the balance, or to where and how the watch is being worn. A watch that loses several seconds or more a day is worth investigating, because slow running is the classic early warning that a movement is tiring.
The four most common reasons a mechanical watch runs slow, roughly in order of likelihood:
- Low amplitude from old, dry oils. As lubricants degrade, friction rises and the balance swings less freely. This is the textbook signal that a watch is due for service, especially if amplitude has dropped well below 250 degrees.
- Resting in a slow position. Positional variation is normal; a watch can run noticeably slower dial-up or crown-down than on the wrist. If it only loses time overnight on the nightstand, try resting it in a different position.
- A nearly unwound mainspring. As the spring runs down, torque falls and the watch slows in its final hours of reserve. An automatic that sits unworn or a manual you forgot to wind will both drift slow before stopping.
- Regulation set slow. Like the fast case, the watch may simply be adjusted a hair slow. This produces a small, consistent loss that a regulator nudge can correct.
Of these, falling amplitude is the one to take seriously. The other three are situational or cosmetic, but a movement that has lost energy because its oils have aged will only get worse until it is serviced.
04Diagnose it: measure before you guess
Guessing wastes money. A demagnetizer will not help a watch that needs a service, and a service will not undo magnetism. The only way to know which path you are on is to measure, and that is exactly what a timegrapher does: WatchScope turns your phone into one, reading rate in seconds per day, amplitude in degrees, and beat error in milliseconds straight from the ticking of the movement.
Take readings in several positions and the pattern tells you the cause. A fast rate with normal amplitude points to magnetism or regulation, both quick and cheap to address. A slow rate paired with low amplitude points to worn lubricants and an imminent service. Large swings between positions add detail about wear and poise.
Two readings settle most cases. Rate tells you the direction and size of the error; amplitude tells you whether the movement still has the energy of a healthy watch. Together they decide whether you reach for a demagnetizer, a regulator, or a watchmaker.
05Fixing it: demagnetize, regulate, or service
Once the numbers point to a cause, the fix follows directly. For a fast rate that resolves with a magnetism check, a demagnetizer is the answer: place the watch on the pad, press the button, draw it slowly away, and re-measure. It is the cheapest and most satisfying fix in watchmaking, and it often restores a watch to within seconds a day instantly.
A small, steady offset in either direction with healthy amplitude is a regulation job: a careful nudge of the regulator arm brings the rate back to zero. A falling-amplitude, slow-running watch is a service case, and no amount of regulating will save it; a watchmaker will clean and re-oil the movement to restore energy and accuracy. Match the cause to the fix and you avoid paying for work the watch did not need.
Frequently asked questions
Why is my mechanical watch running fast?
The most common cause is magnetism, which makes the hairspring coils stick and speeds up the balance, often adding tens of seconds or minutes a day. Less commonly it is over-amplitude with knocking, or a watch simply regulated a little fast. Check magnetism first with a demagnetizer before suspecting anything else.
Why is my watch running slow?
Slow running usually means the balance is not getting enough energy. The classic cause is low amplitude from old, dry oils, which is the standard signal that a service is due. It can also be resting in a slow position, a nearly unwound mainspring, or regulation simply set slow.
Is it normal for a watch to gain a few seconds a day?
Yes. A few seconds a day, fast or slow, is completely normal for a mechanical watch and well within factory tolerance for most movements. Only large deviations of tens of seconds or minutes a day indicate a specific problem worth diagnosing.
Can magnetism make a watch run fast?
Yes, and it is the single most common reason a watch suddenly gains time. Magnetised hairspring coils cling together, effectively shortening the spring, so the balance oscillates faster. A fifteen-euro demagnetizer fixes it in seconds, which is why it should always be the first thing you rule out.
How do I fix a watch that runs fast or slow?
Match the fix to the cause, which you find by measuring. A demagnetizer cures magnetism-driven fast running, a small regulator adjustment corrects a steady small offset in either direction, and a watchmaker service restores a slow watch with falling amplitude. Measure rate and amplitude first so you do not pay for work the watch does not need.
Find out why in two readings
Download WatchScope free on Android to read your watch rate, amplitude, and beat error and pinpoint the cause.