The ISO 6425 standard for ‘Divers’ watches,’ as formulated by the International Organization for Standardization, was first released in 1982 and last updated in 2018. The current 7-page standard outlines the international requirements for what constitutes a ‘water-resistant watch’.
The ISO standard stipulates that it “specifies requirements and test methods for divers' watches. Saturation divers' watches for use in deep diving are addressed in Annex 1 of the standard”.
And therein lies a little problem: very few watches meet all the requirements of the ISO standard.
However, the ISO standard is a good starting point, if only to raise factors you may not have considered. It can also allow you to decide whether you need to invest in a dive watch that is ISO-certified.
So, what does the ISO standard stipulate as factors essential to a dive watch? Sections 6 and 7 of the standard provide most of these factors, which include:
- The time on the watch face must be visible at all times, with the minute’s hand clearly distinguishable from the hour hand.
- The watch must be equipped with a device that the diver can use to pre-select up to 60 minutes of time.
- The time set on the pre-selected device must be visible.
- The above can be in the form of a rotating bezel or a digital display.
- Said display must show 60 minutes with markings indicating every 5 minutes.
- The watch-keeping time (i.e., in good running order) must be clearly visible.
- Battery-powered watches must have a visible low-battery indicator.
- All the above requirements must be visible at a minimum of 10 inches (25 cm) at a depth (i.e. in the dark).
- Salt-water resistance must be tested by which the watch is placed in a sodium chloride solution of 1.05 ounces per 0.26 gallons (or 30 grams per liter) for 24 hours at 64 to 77ºF (or roughly 18 to 25ºC). The watch case should thereafter be inspected for adverse changes, such as oxidation, as well as moving parts tested for functionality.
- There must be a test of resistance to thermal shock. In this test, the watch is immersed in hot water (at 104ºF or 40ºC), then placed in cold water (at 41ºC or 5ºC), and then back into hot water. Here too, the focus is on whether moisture has entered the watch.
- There is also a complex ‘reliability underwater’ test, which essentially tests whether the watch can withstand undue leakages.
- A further test is that for shock-resistance, which is akin to the watch being dropped from a height of one meter onto a hardwood floor. It too is quite a complex test in its execution.
Suffice to say that failure of any of these tests means the immediate failure of that watch model being designated as a dive watch.
A watch that passes all of these ISO-mandated tests has earned the right to be marked with the word ‘Divers’ followed by the depth rating in meters. An example would be 'Divers 300m.'