The international standard ISO 764 Horology--Magnetic resistant watches defines the resistance of watches to magnetic fields. According to ISO 764 or its equivalent DIN 8309 (Deutsche Industrie Norm - German Industry Norm), a watch must resist exposition to a direct current magnetic field of 4,800 A/m (amps per meter). The watch must keep its accuracy to +/-30 seconds/day as measured before the test in order to be acknowledged as a magnetic resistant watch. “Annex A” of ISO 764 deals with watches designated as magnetic resistant with an additional indication of intensity of a magnetic field exceeding 4,800 A/m.