Its history dates back to 1846 where experiments done to create anti-magnetic watches were first recorded. It was Vacheron Constatin, a premier watch-making company who had first done the study and experimentation. However it was only decades later until it was actualized. They were able to develop a watch that can endure magnetic fields because they used non-magnetic metals. They used the metal Palladium for their balance wheel, balance spring and lever shaft making these watches still able to function even within or after high magnetism.
Charles Edouard Guillame was the one who discovered Invar and Elinvar, nope they are not islands, but nickel based alloys that are able to withstand magnetic fields allowing a watch to remain accurate. Other alloy-based materials also include Glucydur and Nivarox which were widely used by watchmakers in the 1950’s.
Aside from using alloys, another method of producing non-magnetic watches is by using a highly conductive material to house the movement inside a case.
As mentioned earlier it was Vacheron Constantin that first developed these watches; in 1915 they introduced the first anti-magnetic pocket watch. It was then followed by Tissot’s non-magnetic wristwatch in 1920, and then the first anti-magnetic chronograph by Vacheron Constantin in 1954. The company Jaeger Lecoultre improved the chronograph’s design and improved its resistance by doubling-up the case.
Today an international standard which is the ISO 764 dictates that this type of watch should be able to sustain itself from direct current magnetic field exposure of 4,800 Ampere per meter. It also states that it should maintain its accuracy to give or take 30 seconds/day as calculated before the test for it pass as a magnetic-resistant watch. An additional soft-iron clasp is also used to cover the movement to ensure that magnetic fields are not formed inside the watch.