About ISO 6425 for Dive Watches: A Comprehensive Resource

What does it mean when a dive watch is ISO 6425 certified? Here’s everything you need to know.

I love dive watches. In fact, my everyday watch is a 36-millimeter Omega Seamaster, and my “dress watch” is a sparkly 28-millimeter Seamaster. I have loads of respect for bands who make divers for small wrists. 

If you love these ocean-faring timepieces as much as I do, you may have come across the phrase ISO 6425. Heck, even if you’re a casual sport watch fan, you’ll likely have come across it. Many of the best dive watches out there may claim they’re built to ISO 6425 standards or are ISO-6425-certified.

So what does this mean? Is it important? Here’s everything you need to know about this watch standard.

Where Did the ISO 6425 Standard Come From? A Little History

Let’s start with a little dive watch history. ISO 6425 was developed in 1982 as a response to the growing dive watch industry.

For a long time, SCUBA diving was reserved for professionals. This means only military personnel, scientists, and other service members had any need to SCUBA dive. In the 1960s, brands like Rolex, Blancpain, and Zodiac developed watches that could handle such depths and pressure.

Divetronic AG developed the first dive computers in the 80s. They were more accurate and reliable. Dive watches, initially essential tools that people’s lives depended on, became fun accessories. Brands started selling dive watches, dive-style watches, and even watches that looked like divers, which sometimes didn’t even have 100 meters of water resistance.

If there’s one thing we do know about watch lovers, it’s that they love a lot of functionality. Well into the quartz crisis, we no longer even needed automatics. Nowadays, we don’t even need watches to tell time. This is irrelevant to dive watch fans who still want their dive watches to handle proper diving — even if they’d never subject it to such activity.

More importantly, some divers might consider these watches a contingency plan. Of course, if you’re a recreational diver and your dive computer malfunctions, you should simply call it a day. Don’t go swimming around thinking you could use your Submariner instead of the computer.

The International Organization for Standardization stepped in to quell the confusion. By creating the specific rules and tests to ensure a dive watch was an actual one, collectors and divers alike would know what to look for. Watch brands welcomed this as a way to market their offerings as more legitimate, or at least more spec-forward. We watch collectors love our specs.

What Is ISO 6425 Certification?

ISO 6425 is a standard set by the International Organization of Standardization. After comprehensive studies, the organization set these standards to qualify what makes a watch perfectly suitable for diving. Fortunately, ISO outlines everything on its website. The hyper-specific standards include how to test the watch and in what order.

The most important requirements include water resistance, a dive time indicator, and magnetic resistance to another ISO standard. As you can see, there are layers of standards on top of layers of tests. The standard has been repeatedly updated, first in 1984, then in 1996, and again in 2018. 

Important ISO 6425 Standards

First and foremost, the watch must be water resistant to 100 meters. This is a given since no proper watch brand would label their watch a diver unless it at least met this standard. Even most vintage dive watches, if they’re a professional model, will be resistant to 100 meters. In fact, ISO’s required testing involves keeping the watch submerged for 48 hours, ensuring it stays operational.

Second, the watch must have some way of measuring elapsed time. This usually comes in the form of a rotating bezel. Timing is all-important in diving. Obviously, you can only spend a limited time underwater. Even more, if a diver ascents too quickly, the nitrogen gas in their body will expand and be difficult to eliminate.

Relatedly, ISO requires manufacturers to protect the timer from “inadvertent handling.” This is why dive watch bezels are unidirectional. If you accidentally turn your timer and don’t realize it, it’ll at least overestimate your time spent underwater. If the bezel were bidirectional and you accidentally moved it clockwise, it would be a disaster if you thought you had more time than you did.

Another requirement is clear markings indicating every five minutes on the bezel. Even if the mark is on only every ten with Arabic numbers, there’s at least usually an indicator in between them. Watches like the Seiko Prospex SJE093 Skin Diver or even the Submariner are good examples. 

The ISO also requires the watch to undergo condensation tests, shock resistance tests, temperature tests, corrosion tests, and pressure tests. The crown must handle water pressure equal to 25% or more of the watch’s water resistance. After all, if the crown doesn’t seal properly, the case’s imperviousness will be compromised. 

The shock resistance tests include being hit twice by a hammer with a specific weight at a specific velocity. It also includes being dropped one meter onto a horizontal hardwood floor. Meanwhile, certification experts test the corrosion resistance via a salt spray assessment.

Other ISO Standards

Two other standards are required to meet ISO 6425 standards. First, ISO 764 requires a watch to resist a magnetic field of 4800 A/m. Even when exposed to a direct current, it must maintain its accuracy of plus or minus 30 seconds a day. Then, ISO 17514 requires a watch to pass a legibility test. The diving time and bezel, among other features, must be visible in the dark after light exposure for 180 minutes. This tests the contrast of the watch as well as its lume.

Certification vs Compliance

So here’s the thing: most brands don’t even bother to build their divers to ISO 6425 standards. Neither the Rolex Submariner nor the Omega Seamaster are. Though it would be a boring initiative, I bet you can still side-by-side the features of a luxury diver with the requirements of ISO 6425. Likely, there would be a lot of overlap. It seems Swiss hard-hitters prioritize Chronometer certification over ISO 6425.

Even more, there’s a difference between watches built to ISO 6425 standards and ones officially certified. You’ll find more of the former than the latter. In fact, the International Organization for Standardization doesn’t do the certifying. They’ve simply created the standards and tests.

The ISO has a committee that accredits third parties to do the certification. Over 1,000 third parties can certify a watch for ISO 6425. Omega turns to METAS, or the Swiss Federal Institute of Metrology, for its Chronometer certification. They also happen to do ISO 6425 certification. The Omega Seamaster Planet Ocean Ultra Deep is the brand’s sole ISO-6425-certified diver. Sinn is another brand that famously offers certified watches.

Meanwhile, brands like Certina, Helm, and Citizen build ISO-6425-compliant watches. They do their own testing in-house but don’t seek official certification. Seiko ensures that many of its divers are ISO-6425-compliant. However, the brand doesn’t disclose whether or not they subject the watches to the stringent tests that the International Organization for Standardization requires.

Conclusion: A Flex but Not Required

It’s undoubtedly cool that a watch company offers ISO-6425-certified watches. I would 100% say it’s a major feather in the watch’s cap. It gives it a sense of legitimacy like it’s a true piece of diving equipment.

However, as many popular divers prove, it’s not a prerequisite for a good dive watch. In fact, most collectors would prefer Chronometer-certification. Still, brands are more likely to upcharge significantly because of Chronometer status, to an extent they wouldn’t for ISO 6425 status. I say take what you can get in every price category.

Questions? Comments? Let me know below!