What is a dive watch?

Buffy Acacia

Coming into the world of watch collecting can be confusing for a beginner, as watch enthusiasts have developed a small lexicon of their own. Although something like “dive watch” sounds pretty self-explanatory, there are multiple decades of history and development behind this genre and why it has become one of the most popular. Even the humble Casio F91W with its 30m of water resistance has been pressure tested to depths beyond 200m, but does that make it a dive watch? Let’s break it down and find out.

The ISO standards defining a “dive watch”

Some collectors will tell you that a dive watch must conform to the ISO 6425 standards, and so will many brands that abide by them. The ISO (International Organisation for Standardisation) essentially provides reliable and certifiable methods to ensure quality and repeatability across all kinds of global industries. ISO 6425 provides these minimum requirements and tests:

• Equipped with a diving time indicator (e.g. rotating bezel, digital display, or other). This device shall allow the reading of the diving time with a resolution of 1 min or better over at least 60 min.
• The presence of clearly distinguishable minute markings on the watch face.
• Adequate readability/visibility at 25cm (9.8in) in total darkness.
• The presence of an indication that the watch is running in total darkness. This is usually indicated by a running second hand with a luminous tip or tail.
• Magnetic resistance. This is tested by 3 exposures to a direct current magnetic field of 4,800 A/m. The watch must keep its accuracy to ± 30 seconds/day as measured before the test, despite the magnetic field.
• Shock resistance. This is tested by two shocks (one on the 9 o’clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3kg hammer with an impact velocity of 4.43 m/s. The change in rate allowed is ± 60 seconds/day.
• Chemical resistance. This is tested by immersion in a 30 g/L NaCl solution for 24 hours to test its rust resistance. This test water solution has a salinity comparable to normal seawater.
• Strap/band solidity. This is tested by applying a force of 200 N (45 lbf) to each spring bar (or attaching point) in opposite directions with no damage to the watch or attachment point.
• The presence of an End Of Life (EOL) indicator on battery-powered watches.
• A water resistance of at least 100m/10ATM

If a watch meets the criteria of ISO 6425, then you can be certain of its performance when diving. It also earns the right to have the word “DIVER’S” on the dial, which non-conforming watches cannot. By that logic, the Casio F91W definitely isn’t a dive watch, but then neither is the Rolex Submariner — definitively the most famous dive watch of all time. ISO 6425 wasn’t even established until 1996, meaning that you could be discounting all of those incredible vintage divers.

Clearly, we can’t rely on standards as a pure definition. Watches that were purposefully built for diving were introduced in the 1930s; however, the elapsed-time bezel wouldn’t surface until the 1950s with the Rolex Submariner and Blancpain Fifty Fathoms. This is the style that really took off, as waterproofing technology and being able to time dives underwater made scuba diving much more mainstream. Watches like the Submariner and Fifty Fathoms have been copied and homaged an infinite number of times, but they were the first in a long line.

The reality is, few people who own dive watches will actually take them diving, so owning a “dive-style” watch with low water resistance isn’t as much of a faux-pas as some may suggest – unless they actually took it diving. For example, the Chanel J12 X-Ray looks like a dive watch, but I pity the person who mistakenly takes such an expensive watch under water merely because it has a timing bezel.

What you should look for in a dive watch

So, what do watch enthusiasts look for in a dive watch? The first key aspect is obviously water-resistance. For many, a proper dive watch must have a water resistance of 200 metres or more. This is because the stresses of ocean currents and underwater movement can actually cause spikes of pressure, unlike the still atmosphere of a static pressure test. The most common suggestion is that 100m is more suitable for casual swimming and snorkelling, while 200 metres is necessary for scuba diving. The usual maximum depth for scuba diving is only 40 metres, but a watch with 50 metres of water-resistance or less is rarely recommended for anything other than splashing or rain. Whether or not these guidelines are accurate is a matter of great debate, and ultimately, your level of comfort will dictate how deep your watch will travel.

Another key element is a screw-down crown. Being one of the most vulnerable points of a wristwatch, a screw-down crown helps mitigate concerns of being left in an open position where moisture and debris could get inside and wreak havoc. A push-pull crown does not disqualify a watch from recreational underwater adventure, but a screw-down one affords that additional level of security that any dive watch worth its salt needs, as it can’t be opened by accident. Though not known for being a dive watch brand, Nomos has an excellent crown system in which the crown tube is red – a visual indicator that your crown has not been screwed down all the way if you can still see red.

Panerai, a brand synonymous with diving, has a signature characteristic in its Luminor collection with their crown safety lock system. Most brands have simply introduced crown guards to protect the crown from shock and bumps even better, but Panerai has a devised a lever-operated safety lock that only allows the crown to be unscrewed once the lever is lifted, adding another layer of protection.

These days, it’s not uncommon to see people wearing their dive watches on leather straps, though this is just as much a result of vintage bracelets stretching beyond repair as it is a stylistic choice. For a vintage piece that has retired from its days in the ocean, it makes sense. But for your modern dive watch itching to get in the water, a leather strap would be criminal. Leather and water don’t play nicely, and it will severely damage the leather over time, especially if it’s salt water.

For aquatic adventures, you really want to have something that’ll hold up in water. Different textiles, rubber, or metal bracelets are what you’re looking for, and when it comes to something like NATO-style or rubber straps, you can easily change the fit should you wish to wear them over a dive suit.

Bracelets, though far easier to clean after dives, can be a bit more complicated. A basic bracelet, once sized… well, that’s pretty much it, and even toolless micro-adjust systems often don’t offer enough extension to fit a wetsuit. That is why many reputable dive watch manufacturers offer bracelets with a diver’s extension at a minimum. This rudimentary system will allow you to extend the length of the bracelet by unsnapping a folded piece of metal within the clasp, though not offering finer adjustment.

Watchmakers like Tudor have been praised for having more complex divers’ clasps. The recently released Pelagos Ultra, for example, has a spring-loaded system that allows the bracelet to stretch and contract as needed. Rolex’s Glidelock system on its Submariner Oyster bracelets allows ten 2mm increments of adjustment, while the Deepsea Challenge’s Glidelock extends that to 26mm total.

These on-the-fly adjustment systems have become favoured by watch collectors, and not just for the purpose of diving. The reality is that a bracelet with a system like Glidelock or Tudor’s T-Fit ensures your watch fits perfectly year-round as your wrist contracts or expands with changing temperatures.

Final thoughts

While true definitions of dive watches remain elusive, there is definitely a vibe that they all have in common. Apart from having a serviceable level of water-resistance, a rotating bezel is the most immediately recognisable feature (although some exist without one), as is a general ruggedness to the case. The dials are generally legible with large, luminous markers, and ISO certification can be helpful as an extra layer of assurance. But if you’re looking for a dive watch that suits your needs, you only need to go with your gut.