What is a Dive Watch?

What is a dive watch? Divers watch with black rubber strap

What is a Dive Watch?

There is a big difference between a water resistant watch – even a watch that is water resistant to 200 metres – and a watch that is suitable for diving. But what is a dive watch?

To be classified as a Dive watch, a watch must conform to ISO 6425 – this is a series of tests that check whether the watch performs accurately under intense dive conditions – conditions that almost all divers will never go anywhere near reaching.

A dive watch can have an automatic or quartz (battery) operated movement – most are automatic.

History of Dive Watches

Initially watches were tailor-made for their owner to meet their specific requirements as, prior to the 20th Century it was only a select few who wore a watch.

In past times, when divers wore hard hats, they would often take their pocket watches with them inside their helmets!

It was after World War I that wrist watches became popular and they quickly become and item that many relied upon.

Explorers, adventurers, those in the military and those who took part in sports were no exception and therefore, it became quite a focus for watch companies to produce watches that could endure these trials and, in particular, not let in water.

The trickiest part of a watch to keep sealed from water ingress is the crown.

Rolex Oyster

Rolex produced the first rugged underwater watch. Called the Rolex Oyster, this hermetically sealed case design with a screwed-down crown was patented by Hans Wilsdorf, the owner of Rolex, in 1926.

In 1932 a British woman called Mercedes Gleitze swam the English channel with one hanging on a ribbon from her neck. She wore it in the water for 10 hours and it kept perfect time throughout her swim.

Hans Wilsdorf capitalised on this wonderful achievement and the subsequent marketing catapulted Rolex’s standing in watch making. It was this watch and this event, and the marketing off the back of it that made Rolex a household name and was a huge coup in marketing tactics. The Rolex Oyster is arguably the single most important watch in Rolex’s history.

The Omega Marine was the first commercial divers watch. Although mainly for professional divers it was made to withstand depths of up to 135m.

The Italian Royal Navy requested a dive watch which was to be luminous and this was supplied by Panerai after Rolex made the watch for them.

In 1954 the Rolex Submariner was the first properly commercially produced dive watch for the public.

What is a Dive Watch?

ISO 6425

In 1996 the International Standardization Organization (ISO) devised a set of criteria to classify a watch as having passed the standards set for a dive watch. If a watch is tested, and passes, the ISO 6425 standards, then the watch is permitted to use the word “DIver’s” on the dial of the watch.

A watch brand will put their watch forward to undergo these tests thereby ensuring the status of their watch. Not all watch manufacturer’s will put “Diver’s” on the dial, despite it having met all the requirements – Rolex being one.

The ISO 6425 set of standardizations are comprised of the following tests:

1. Water Resistant to 100 metres.

Not only should a watch be water resistant to 100m but it must also remain accurate at this depth. Most divers will never go to a depth of 100m but this is the depth to which the ISO 6425 is required to perform.

The tests carried out in stationary conditions with new watches and new seals. Therefore, many dive watches surpass this standard and are water resistant to 200 meters.

Some watch manufacturer’s go much further (quite literally!) than this! A Rolex Deep Sea Sea-Dweller is 3,900m rated whilst an Omega Ultra deep Professional is water resistant to 15,000m!

A Screw-In Crown

A screw-in crown helps the water resistant as it forms a seal when screwed in – much more so than a push crown. Of course, you should never unscrew the crown when underwater. The crown is the most vulnerable part of the watch in relation to water ingress so this posed quite a problem to watch manufacturer’s in the early days.

A Screw Back

A screw back also ensures the seal is unbroken and secure.

A Domed Glass

Whilst not essential, a domed glass also help to withstand underwater pressure.

2. Uni-Directional Rotating Bezel.

A safety feature for a diver is that they must know how long they have been submerged under water for – this is to ensure they don’t lose track of the time. This ensures that the diver does not run out of air mix and lead to compression sickness – commonly known as “the bends”.

The time is tracked for a period of up to an hour as most dives are under this and, even if they go just over, the diver will know that an hour has already lapsed plus the minutes showing on the bezel.

A uni-directional bezel only rotates in one direction. This is important as it doesn’t allow for any accidental movement, say from a knock, of the bezel in the opposite direction, which could lead to a diver being shown he hasn’t been as long under water as he really has.

With a uni-directional bezel, should the bezel get knocked it will show the diver as being under for longer (never shorter) than he has. Hence keeping him or her on the safe side of the error.

As the diver begins his descent into the water he should rotate the bezel so that it lines up with the minute hand. He can then, at any time, glance at his watch and will know how many minutes have elapsed since she or he started the dive.

3. Luminescent Hands and Markers

The deep sea has very limited visibility and some waters are worse than others. Therefore the tips of the hands and the markers/batons are often painted with a luminous paint.

The visibility test should mean the watch is legible at distances of 25cm in total darkness.

There must also be a luminescent second hand – this will show the diver that the watch is still working.

There should always be four points that a dive watch should be luminescent – in particular the 12 o’clock position will be prominent as it is easy to lose a sense of direction underwater.

4. Materials of the Case and Strap


The materials of dive watches need to be strong and durable to withstand not just the pressure of the water but the cold and the salty composition.

Surgical stainless steel and titanium are excellent materials to withstand these pressures.

Straps will be either stainless steel or rubber, both of which have been shown to withstand pressure, saltwater and are strong.

Pressure and Impact

The pressures under water are quite intense and dives can involve occasional knocks and scrapes. Therefore the ISO 6425 test also involves knocking the case at the nine-o’clock position and the glass on a watch with a plastic hammer, to the degree of 5,000gs to ensure it doesn’t crack, break or affect its accuracy. The tolerance allowed is +-60 seconds a day.

As already mentioned, the crown is a weak area on a watch. This is further tested by applying a weight of 5 Newtons for 10 minutes to the crown at a depth of 125% of its water resistance (for instance 125m on a 100m watch).

Temperature Fluctuations

The watch must withstand drops in temperature (it can get VERY cold in water). So the watch will be placed in water which is heated to 40°C, then the water temperature is reduced in to 5°C, then increased again. Each temperature is held for 5 minutes.

The accuracy must, once again, hold – despite all the metal parts expanding and contracting as this happens.

Rust Resistant

The watch must be chemically resistant to rust. To test this, the watch is submerged in a chemical solution comparable to salt water for 24 hours, after which it is removed from the saline solution and is checked for rust.


The watch must be shown to be magnetically resistant. To test this, the watch is subjected to bursts of a magnetic field and must, once again, keep its accuracy.

Concluding the Tests

When all these tests have been carried out, the watch is then laid on a plate and heated. Then a drop of moisture is applied to the glass.

It is then checked for condensation or leaks – any hint of this and the watch will fail the test.

Helium Escape Valve

The most extreme dive watches also have what is called a Helium Escape Valve, allowing helium gases to escape and so protect it from damage to the crystal.

To Sum Up

As you can see, in answering the question “what is a dive watch?”, a watch manufacturer must meet very strict standards.

It is no mean feat for a watch manufacturer to not only produce a 200m watch but to produce one that conforms to the ISO 6425 standards to allow it to display “Diver’s” on the dial is quite an undertaking.

It’s a stamp of quality with a seal of approval as to it’s accuracy and durability.

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