What really makes a Diver’s watch?

Dive watches these days are not few and far between. Since the release of the Rolex Submariner, the first true dive watch, in 1954 the popularity of watches suitable for high pressure submersion has increased as diving with Self Contained Underwater Breathing Apparatus (SCUBA diving) becomes a more accessible hobby. However, look around any watch store and you will notice that countless watches are fitted with rotating timing bezels and water resistances marked to “100m”, what should be plenty for the conventional diver if true! But those with experience in the world of horology know that not all diving watches are created equally, today we’ll take a look at just that.

ISO 6425:

Thankfully, the answer to the key question within this blog post seems simple! International Organization for Standardization standard 6425! The International Organization for Standardization, more commonly known as ISO, was established in 1947 and gives specifications for services, systems and products. Since its conception ISO have published 22689 standards. It is standard ISO 6425 that sets out:

requirements and test methods for divers’ watches and for saturation divers’ watches for use in deep diving (see Annex A which deals with watches for saturation diving).

It applies to divers’ watches designed to withstand diving in water at depths of at least 100 m and equipped with a secured measuring system to indicate the diving time, which is visible in darkness.

Moreover, it indicates the marking which the manufacturer is authorized to apply to them” ISO.org

To Obtain an ISO 6425 requires rigorous testing of the watch to ensure its reliability, if you aren’t much interested in the technical ins and outs of the ISO 6425, go ahead and skip to the next sub-heading to save yourself the reading!

Beginning with the condensation test, with the watch being heated to 40-45 degrees C and a drop of water at 18-25 degrees C placed on the watch glass, being removed after 1 minute. this test is repeated multiple times in the testing and if at any point the watch develops condensation on the interior of the crystal it is disqualified.

Following this test is the reliability in water test, with the watch being submerged in 30cm of water for 50 hours and followed up immediately by a repeat of the condensation test.

Next, potential weak points in the case are tested such as the crown. The watch is subjected to an overpressure of 125% (so for a Diver rated to 200m, it would be pressurised to the equivalent of 250m) applied within 1 minute, for 10 minutes. And to an external force of 5N perpendicular to the crown and pushers (if any). Again followed up by a repeat of the condensation test.

Water tightness and resistance to over pressure is then fully tested, with the watch again over pressurised to 125% within one minute but now maintained for 2 hours. Subsequently, the over pressure will be reduced to 0.3 Bar within 1 minute and maintained for 1 hour. Any evidence of water intrusion or condensation is a fail. The 125% overpressure is to ensure the watch is not over pressured during fast wrist movements like swimming at depth which could add an extra 50kPa of pressure (the equivalent of 5m of depth).

Resistance to thermal shock is then tested, the watch is submerged in water at 40C, 5C and back to 40C. Spending 10 minutes in each temperature with a maximum of 1 minute transition between temperatures.

There are very specific aesthetic and movement design specifications as well.

The main being the presence of a time-preselecting device such as a specifically marked unidirectional bezel or clearly visible digital display that should be protected against unintended adjustment. 

The following items must be visible from 25cm away in the dark: an hour hand clearly distinguishable from the minute hand, the set time of the time-preselecting device, indication the watch is running (most commonly in the form of a lumed seconds hand tip or tail) and an end of battery life indicator in the case of battery powered watches.

Regarding movement specs, the watch is tested in 3 expositions to a direct current magnetic field of 4,800A/m maintaining an accuracy of +/-30 seconds a day as measured before the test despite the magnetic field. (I.e if the watch was running at +9 seconds a day before the test and running at +39 after the test it would still be a pass).

The shock resistance is ensured by two shocks on the 9 O’clock side and dial delivered by a rubber mallet mounted on a pendulum providing a shock 4.43m/s. following the shock a timing tolerance of +/- 60s a day.

The need for resistance to salty water is a given for a diving watch, watches are tested by being immersed in water of a salinity comparable to seawater at 30g/l NaCl (sodium chloride) for 24 hours. Ensuring there is no degradation of the case and hardware, paying special attention to the full movement of the rotating bezel.

The last test the watch is subjected to checks the durability and strength of the strap. This is done by applying a force of 200N (the equivalent to 45lbf) on each mounting point of the strap and ensuring there is no damage.

If a watch passes all of these tests then it is worthy of the ISO 6425 and can be marked with “DIVER’S WATCH xxx M” or DIVER’S xxx M” distinguishing ISO standard dive watches from similar designs not actually suitable for use diving.

PHEW! Now if you’ve already read all the way down to here, consider yourself a dive watch aficionado. The tests to achieve an ISO 6425 are understandably stringent, and even incorporate other ISO tests within them such as ISO 764 concerning anti-magnetic properties and ISO 1413 concerning shock resistance, which I intentionally omitted vast detail on for simplicity. These ISO tests must be satisfied as well as all tests stipulated by the ISO 6425 to be an ISO certified dive watch.


Surely, after all that, that’s the end of it! the question has been answered right? Wrong! The vast majority of dive watches aren’t ISO 6425 certified. So where does that leave us? While ISO certification is an assurance of quality and performance it is not an exclusive mark of an effective dive watch. And most brands undergo their own testing to certify their pieces. Some, often exceeding the standards of the ISO tests and offering warranties that cover any issues relating to water ingress due to a failure of the watch.

To prove our point, we have with us 2 of the best diver’s watches that money can buy. Both of which are not officially ISO certified, and as you will quickly see this does not signify a lack of quality or functionality!


the first and most striking of today’s watches is the Oris ProDiver Chronograph 51mm (01 774 7727 7154). Fitted with Oris’ patented rotation safety system that locks the bezel to prevent any unwanted bezel movement. An accidental adjustment of the bezel could prove fatal when working at the depths allowed with the Oris ProDivers, this piece being certified to operate as deep as 1Km (1000 meters) underwater. It’s impressive size shows it means business too, at 51mm across and impressively tall as well, visually this watch is built for professionals. It is likely with such an astonishing depth rating that the testing of the Oris ProDiver would well exceed the parameters set out by ISO.


Our next piece is assuredly known by Divers all around the world. Rolex figuratively and literally hold the crown for making dive watches for decades. The Rolex Submariner and Later the Rolex Sea-Dweller boasting even deeper water resistance had gained the trust of professional Divers over 43 years before the first release of ISO 6425. And the same trust remains today.


Having the level of quality set by the ISO 6425 standard leaves a benchmark for assured performance when buying watches that must perform under the rigours of professional diving. However, when buying watches that not only satisfy the requirements of the standard (which only requires a certified water resistance of 100m) but exceed it significantly, like both our pieces here. With 10X deeper water resistance than would satisfy the ISO 6425 regulations. Here, the standard set by the brands that are producing these incredible watches, continually refining and guaranteeing their abilities is just as much of an assurance of deep sea survivability as any ISO standard!

If you want to be the next owner of either of these impressive watches, view them to buy at our Pre-Owned site https://www.thewatchsource.co.uk/preowned/ Or, to simply enjoy these stunning pieces, view our extensive in-house photography of the watches below in the Gallery.

Be sure to follow The Watch Source blog for instant email notifications when we publish new releases! Alternatively, like our Facebook, Instagram or Twitter to be the first to know about new releases and other updates from The Watch Source.

Facebook: https://www.facebook.com/thewatchsource/

Twitter: https://twitter.com/WatchSourceUK


Preowned: https://www.instagram.com/watchsourcepreowned/

Main: https://www.instagram.com/watchsource/




Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s