(or attaching point) in opposite directions with no damage to the watch of attachment point. The bracelet of the watch being tested shall be closed. Marking. Watches conforming to ISO 6425 are marked with the word DIVER'S WATCH xxx M or DIVER'S xxx M to distinguish diving watches from look-a-like watches that are not suitable for actual scuba diving. The letters xxx are replaced by the diving depth, in metres, guaranteed by the manufacturer. Diver's watches for mixed-gas diving Diving at a great depth and for a long period is done in a diving chamber, with the (saturation) diver spending time alternately in the water and in a pressurized environment, breathing a gas mixture. In this case, the watch is subjected to the pressure of the gas mixture and its functioning can be disturbed. Consequently, it is recommended to subject the watch to a special extra test. ISO 6425 defines a diver's watch for mixed-gas diving as: A watch required to be resistant during diving in water to a depth of at least 100 m and to be unaffected by the overpressure of the mixed gas used for breathing. The following specific additional requirements for testing of diver's watches for mixed-gas diving are provided by ISO 6425: Test of operation at a gas overpressure. The watch is subject to the overpressure of gas which will actually be used, i.e. 125% of the rated pressure, for 15 days. Then a rapid reduction in pressure to the atmospheric pressure shall be carried out in a time not exceeding 3 minutes. After this test, the watch shall function correctly. An electronic watch shall function normally during and after the test. A mechanical watch shall function normally after the test (the power reserve normally being less than 15 days). Test by internal pressure (simulation of decompression). Remove the crown together with the winding and/or setting stem. In its place, fit a crown of the same type with a hole. Through this hole, introduce the gas mixture which will actually be used and create an overpressure of the rated pressure/20 bar in the watch for a period of 10 hours. Then carry out the test at the rated water overpressure. In this case, the original crown with the stem shall be refitted beforehand. After this test, the watch shall function correctly. Marking. Watches used for mix-gas diving which satisfy the test requirements are marked with