Tool-watch engineering

ISO 764 sets the minimum requirements and the tests for a watch sold as magnetic resistant. Its 1984 edition tested a watch’s exposure to a field of 4,800 A/m, the figure national adoptions of the standard still give.^1, 6, 7

Sinn and Damasko both describe the German standard the same way: a mechanical watch counts as antimagnetic if, after a field of 4,800 A/m, it has not stopped and its rate has changed by no more than 30 seconds a day. That standard, DIN 8309, was withdrawn in 2026 and replaced by DIN ISO 764, the German adoption of ISO 764.^4, 8, 9

Makers go well past the baseline by shielding the movement. IWC Schaffhausen’s Ingenieur of 1955 had an inner case of soft iron that protected it to 80,000 A/m.^10, 11

Magnetic resistance, in amperes per metre

ISO 764 test field4,800^6, 7

IWC Ingenieur, 195580,000^10, 11

Damasko, as Damasko gives it80,000⁸

Damasko says its soft-iron cages reach the same figure. Omega says its Master Chronometer tests, set by METAS, expose each movement and cased watch to 15,000 gauss.^8, 12

DIN 8310 defines water resistance and sets its requirements and tests. ISO 6425 does the same for divers’ watches, which must withstand diving to at least 100 metres, carry a way to measure diving time and stay readable in the dark.^2, 3

Two German makers turned to submarine steel for diving cases: Sinn for its U-series, for the steel’s resistance to seawater and its lack of magnetism, and Damasko for its diving line, in the steel of the German Navy’s Class 212 submarines.^4, 13

Sinn notes that hardness is usually measured on the Vickers scale, because the familiar Mohs scale is not linear; on Vickers, sapphire crystal is around 2,000.⁴

The two German makers took different routes to a hard case: Sinn’s Tegiment process hardens the surface of a steel case, while Damasko’s founder patented a case of hardenable steel that Damasko says is hardened all the way through.^{4, 13, 14, 15}

Shock

Nippon.com describes how Casio’s G-Shock began in 1981 with an engineer’s proposal for a watch that would survive being dropped, and went on sale in 1983 after more than 200 prototypes.¹⁶