Gauss, symbol G, is a unit for measuring magnetic flux density. Watchmakers use it to state how much magnetism a watch can withstand. This matters because strong magnetic fields can change a watch’s balance spring. The higher the figure in gauss, the stronger the field the watch is rated to resist.
How strong is one gauss?
One gauss equals one maxwell per square centimetre. The SI unit of magnetic flux density is the tesla, and 10,000 gauss make one tesla. A rating of 15,000 gauss is therefore the same as 1.5 tesla. Standards sometimes describe the magnetic field in amperes per metre (A/m) instead. A field of 4,800 A/m is about 60 gauss. A field of 80,000 A/m corresponds to a flux density of 1,000 gauss.
How many gauss must an antimagnetic watch withstand?
Under ISO 764, a watch counts as antimagnetic if it withstands a direct-current field of 4,800 A/m, about 60 gauss. Some watches go much further. Rolex launched the Milgauss in 1956 for scientific professionals. Its name refers to its resistance to 1,000 gauss, and the first reference, 6541, carried a rating of up to 1,000 gauss. Omega’s Master Chronometer certification checks that the watch and its movement still work properly in a field of 15,000 gauss.
How is a movement protected from magnetism?
Makers use two approaches. The first surrounds the movement with a soft iron cage. Sinn, for example, uses one in its EZM series. The second builds the movement from non-ferrous materials, so no protective inner container is needed. Omega takes this route to reach high gauss ratings. Its Seamaster Aqua Terra 15,000 Gauss is credited as the first watch with a completely antimagnetic movement. It uses a silicon hairspring. An Omega prototype kept running after exposure to 1.5 tesla.
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