Why mechanical watches gain or lose time

One glance is not enough

A chance comparison shows an accumulated difference without explaining when it arose. For a clearer picture, compare the watch with the same time source at roughly the same hour each day for a week.

Those notes are particularly helpful if you suspect magnetisation or an unusually short power reserve. Compare them with the specifications of your calibre, since different movements have different limits.

You can note wearing hours and overnight position alongside the readings. Instead of “it seems fast”, you will have a useful record of daily gain or loss and how consistent it is.

Overnight position makes a difference

A case keeps changing orientation on the wrist, then spends hours in one position on a bedside table. The balance and escapement can behave slightly differently dial up and crown to one side, affecting the day’s total result.

This is an interesting trait to observe, but it does not replace adjustment. A very large difference between positions warrants a watchmaker’s examination on suitable equipment.

The mainspring has a working rhythm

The mainspring’s torque changes as its reserve runs down. The design aims to maintain even timekeeping, though a nearly empty reserve can produce a different rate from a full one. A consistent winding routine makes comparisons more useful.

Temperature also affects parts and lubricants. Modern materials reduce that dependence, but ordinary daily measurements tell an owner more than experiments with heating or chilling the watch.

When the change is sudden

A sharp change after an impact or contact with a magnetic object differs from small daily variations. Magnetism can indeed make a watch run markedly fast, though similar symptoms can have other causes.

Ageing lubrication and wear affect performance too. If stops or unusual noises accompany the change, simply correcting the hands is not enough; arrange a diagnosis.

Choose the right reference point

Use the exact calibre’s stated tolerance and its measuring conditions. Seiko’s 4R35, for example, is specified at −35 to +45 seconds per day under stated conditions. Other movements can have very different requirements.

A chronometer undergoes a separate testing programme; the term is not a generic name for any accurate watch. If yours consistently exceeds its tolerance or abruptly changes behaviour, bring your readings to a watchmaker. Adjusting the hairspring or regulator yourself is not a sensible shortcut to a few saved seconds.