Why a mechanical watch runs fast

When a mechanical watch suddenly starts gaining a lot of time, the usual cause is magnetism. Near a magnet, the hairspring that governs the balance can become magnetized; its coils cling together, and the watch gains many seconds a day, sometimes minutes. A watchmaker can demagnetize it in a few minutes, usually without opening the case. The other common causes are a knock that has disturbed the hairspring, a regulation that has drifted, the position the watch rests in overnight and lubricants that have aged. Unless the gain is plain to see, the first step is to measure it properly.

Measure the rate first

A measured figure, such as a gain of about twenty seconds a day that grows after nights spent lying flat, tells a watchmaker far more than a sense that the watch runs fast. A week of simple observation provides one.

1. Set the watch to the second against a reliable reference, such as a phone set to network time or the National Research Council’s web clock.
2. Wear it as usual, and at the same hour each day note how many seconds it is ahead or behind.
3. Note how it spent each night: dial up, dial down or on its edge, and whether it was fully wound.
4. After a week, divide the total gain by the number of days. That average, the mean daily rate, is the figure that counts; a single day means little.
5. If the rate seems to change with the overnight position, try a few nights in each position and compare.

Start an automatic from a full wind, by hand where the calibre allows it, since a watch running low on power keeps less regular time.

What counts as fast

A mechanical watch is not expected to keep quartz time, and a few seconds a day either way is normal. The strictest common benchmark is chronometer certification. COSC, the official Swiss chronometer testing institute, tests uncased movements over 15 days, in five positions and at three temperatures. To pass, a movement’s mean daily rate must fall between −4 and +6 seconds. Most mechanical watches are not chronometers and are not held to that. Manufacturers set tolerances for their own calibres, and these can be much wider: Seiko, for instance, gives its 6R20 automatic calibre an accuracy of −15 to +25 seconds a day.

Consistency matters as much as the figure. A watch that gains a steady eight seconds a day is consistent, and consistency is what regulation needs. One that gains five seconds one day and forty the next has a fault worth finding. Even a chronometer’s certificate describes its movement as it was when tested, not after years without a service. A quartz watch is another matter, rated to about ±15 seconds a month; the differences are set out in choosing between quartz and mechanical.

The usual causes

Magnetism

Magnets are everywhere in daily life: in phones, laptops and tablet covers, in speakers, in the clasps of bags and phone cases. A mechanical watch left close to one can stay magnetized after it is moved away, and the clinging coils of its hairspring make it run fast, often erratically. Magnetism rarely does lasting harm. Once demagnetized, a watch usually returns to its former rate. Some modern watches resist magnetism far better than others, through hairsprings of non-magnetic materials or a soft-iron inner case. ISO 764 defines what a watch must withstand to be called antimagnetic: a level of resistance, not immunity.

A knock

A hard knock or a fall can disturb the hairspring so that its coils touch or catch, and the watch then gains heavily. A shock can also damage a balance pivot, which tends to make the rate erratic and different in each position rather than simply fast. None of this shows from outside, and none of it is a repair to attempt at home.

Regulation and position

A watch can simply be regulated a little fast, or drift there over time. Its rate also varies with position, because gravity acts differently on the balance when the watch lies flat and when it stands on its edge. The way it rests overnight therefore shifts the daily average. A small, steady gain can often be offset by resting the watch in a position where it runs slower, a remedy some manufacturers suggest themselves. Temperature plays a smaller part: many mechanical watches gain slightly in the cold and lose slightly in the heat.

Ageing lubrication

As oils thicken and parts wear, the balance swings through a smaller arc. Its amplitude falls, and the rate becomes less stable and differs more between positions. Depending on the calibre, that can show as a gain, a loss, or both on different days. This is not a regulation problem, and regulating the watch only hides it for a while. It is a sign that the watch is due for a full service, which when a watch needs an overhaul describes.

Less common causes

Oil that has reached the hairspring can make its coils stick together much as magnetism does, and the cure is cleaning, not demagnetizing. Too much power can also make a watch gain. With a replacement mainspring too strong for the calibre, for instance, the balance can swing so far that its impulse pin strikes the outside of the pallet fork. Watchmakers call this rebanking, or knocking. The watch gains sharply, usually when lying flat, where the balance swings widest, and the remedy lies in the power, not the regulator.

What a watchmaker will do

A sound diagnosis starts with the quickest explanation. The watch is checked for magnetism and demagnetized if need be. It then goes on a timegrapher, which reads its rate in seconds a day, its amplitude in degrees and its beat error in milliseconds, in several positions. If the amplitude is healthy and the positions agree, regulation is likely to be enough. On most movements a small lever on the balance cock, the regulator, changes the working length of the hairspring; a free-sprung balance is adjusted instead by weights or screws on its rim. If the amplitude is low, or the positions disagree widely, the honest answer is a service, not a regulation that will not hold. A disturbed or oiled hairspring is put right directly.

Keeping it from happening again

Keep the watch away from magnets: off the laptop, away from speakers and magnetic phone accessories, out of bags with magnetic clasps. Keep it wound, or wear it daily, so that it runs on steady power. Take it off for sports with hard impacts. Use the overnight position to correct a small gain. And have it serviced on time, since a movement with fresh oils holds its rate better than one running on tired ones.

If a week of measurement still shows a gain you cannot explain, Viattori’s repair service begins with a free assessment and a written estimate, and no work starts until you approve it. The figures from your week are worth sending with the watch.

Questions

Why is my mechanical watch suddenly running fast?

The most common cause of a sudden large gain is magnetism. After exposure to a magnet, such as a phone, laptop, speaker or magnetic clasp, the hairspring’s coils cling together and the watch runs fast. A watchmaker can demagnetize it in minutes, usually without opening the case.

How many seconds a day should a mechanical watch gain or lose?

It depends on the calibre and its condition. A COSC-certified chronometer’s movement must average −4 to +6 seconds a day in testing; ordinary mechanical watches are not held to that and commonly run several seconds a day, sometimes more. A steady rate matters as much as a small one.

Can magnetism damage a watch permanently?

Rarely. A magnetized mechanical watch runs fast or erratically, but once it has been demagnetized it usually returns to its former rate. If it does not, the movement needs a closer look on a timegrapher.

Should a watch that runs fast simply be regulated?

Only once its amplitude has been measured. If the balance swings healthily and the rate is consistent across positions, regulation will hold. If the amplitude is low, the movement needs a service, and regulating it would only hide the problem for a while.

Does the way a watch rests overnight affect its timekeeping?

Yes. A mechanical watch runs at slightly different rates dial up, dial down and on its edge, so its overnight position shifts the daily average. Resting it where it runs a little slower can offset a small, steady gain.