Antimagnetic
Antimagnetic describes how well a watch resists magnetic fields. Magnetism can make a mechanical watch run fast or stop altogether, and the resistance is rated in gauss or to the ISO 764 standard. A soft-iron inner case or silicon parts add the protection.
At a glance
- Unit of measure
- Gauss or ISO 764
- Protection method
- Soft-iron inner case or silicon parts
- Common magnet sources
- Speakers, magnetic phone or tablet covers, bag closures
Magnetic fields are invisible, yet they go straight to the rate of a mechanical watch: once the steel parts pick up a charge, the watch either runs fast or stops altogether. An antimagnetic watch is built to keep that effect out up to a defined threshold.
How the resistance is measured
The strength of the protection is stated two related but distinct ways:
- Gauss: the intensity of the field a watch can withstand before it drifts
- ISO 764: the baseline pass or fail standard a watch must meet to be called antimagnetic, set at about 60 gauss (4800 A/m) with the rate kept within tolerance
A gauss figure usually exceeds the ISO 764 minimum rather than matching it, so the two are not interchangeable. Below the rated threshold the watch is unaffected; above it, it can still magnetise. It is worth reading this alongside accuracy and deviation, since magnetism shows up directly in the rate, and the calibre simply will not hold its timing.
How it is protected
There are two common methods. The first is a soft-iron inner case around the movement; it draws the magnetic field onto itself and away from the parts that keep time. The second is using non-magnetic components such as silicon, which do not pick up a charge in the first place. Everyday items can carry magnets, from speakers to magnetic phone and tablet covers, clasps and bag closures, though an ordinary phone or laptop rarely magnetises a watch on its own.
For pieces where this kind of durability stands out, browse the Standards category and our guide to the best Japanese watches.
Examples
Resting a watch next to a speaker or a magnetic phone or tablet cover can magnetise an unprotected mechanical watch and make it run fast or stop.
An antimagnetic watch states its durability through a gauss figure or the ISO 764 test it passes, staying unaffected by fields below that rated threshold.
Comparison
A soft-iron inner case and silicon parts add protection in different ways.
| Option A | Option B | Notes |
|---|---|---|
| Soft-iron inner case | Silicon parts | The inner case draws the field onto itself and away from the movement; silicon parts simply do not pick up a charge in the first place. |
Related terms
Frequently asked questions
What does a magnetic field do to a watch?
A magnetic field magnetises the steel parts of a mechanical watch and disturbs its rate, so the watch either runs fast or stops altogether. An antimagnetic watch keeps that out up to a defined threshold and runs unaffected by weaker fields.
How is a watch's antimagnetic resistance measured?
Resistance is stated two related but distinct ways. Gauss is the strength of the field a watch can take before it drifts. ISO 764 is a single minimum threshold, about 60 gauss (4800 A/m) with the rate kept within tolerance, that a watch must meet to be called antimagnetic. A gauss rating usually exceeds that minimum rather than equalling it, so the two are not interchangeable.
What can magnetise my watch in daily life?
Everyday items that carry magnets, such as speakers, magnetic phone or tablet covers, clasps and bag closures, can magnetise a mechanical watch and disturb its rate if it has no antimagnetic protection. An ordinary phone or laptop rarely magnetises a watch on its own. A soft-iron inner case or silicon parts reduce that risk.