The diver’s watch is one of the most celebrated trends in horology

We cannot deny that Diver’s watches are among the most sought-after kinds of timepieces – and the most iconic watch there is has a revealing name: Rolex Submariner.

But apart from this, there is a big confusion over what a diver’s watch truly is, and more, about what does the water resistance shown on the dials and backs of watches truly represent. So we want to shed a bit of light over the matter in order to understand better the key differences that render a true diver’s watch much different from a water-resistant watch.

Ask yourself what a “dive watch” really is!

There is an important difference from a water-resistant watch and a diver’s watch, as every watch has a water resistance.

It is part of the game, that is. Even a dress watch has some sort of minimal water resistance – which usually lies in the range of 3 bar (around 30 meters). This means that saying that a watch has a “water resistance” is not enough – as water resistance alone does not make a diver watch. And if we search a little bit more, we find out that for a watch to be called a diver’s watch, a timepiece has to comply with a very specific set of parameters which are stated in an ISO certification: ISO 6425, to be specific.

The minimum requirements for mechanical diver’s watches (quartz and digital watches have slightly differing readability requirements) are the following (per wikipedia):

  1. 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.
  2. The presence of clearly distinguishable minute markings on the watch face.
  3. Adequate readability/visibility at 25 cm (9.8 in) in total darkness.
  4. 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.
  5. 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.
  6. 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 3 kg hammer with an impact velocity of 4.43 m/s. The change in rate allowed is ± 60 seconds/day.
  7. 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.
  8. 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.
  9. The presence of an End Of Life (EOL) indicator on battery powered watches.

Please note that there is no water resistance minimum stated: however, since the whole affair of diver’s watches started with the production of the first Submariner and Fifty Fathoms, the minimum viable water-resistance for a diver’s watch is assumed to be 100 meters (10 bar). These watches are the oldest: current diver’s start with a 20 bar (200 meters) water-resistance.

Who’s ensuring these characteristics are respected?

Everyone can make watches  that comply with these specs, but “official” divers are similar to “chronometers”: to be officially called like this, they need to be certified by an external, independent organization.

So, in the case of ISO-compliant watches, these tests have to be administered by an officially-certified laboratory – and have a cost of issue.

This means that companies cannot simply state they make a diver’s watch: they should have a proof of it to be so. It also means that not every manufacturer present their watches for certification according to this standard, so they just state that they are compliant and that’s enough. However, they cannot use the official denomination of “Diver’s watch” – which is usually displayed on the dial, when present.

But this first difference takes us to the real meaning of the number that we see on the dial – that is, water resistance.

One of the main issues about water resistance is understanding what it indicates. People routinely buy 30-meter water-resistant watches and then splash into a pool, with water getting into them – and getting the watch-wearers undoubtedly puzzled, to say the least.

Divers watches and water-resistance

The levels of water resistance that we see indicated in a watch measure the maximum depth that a watch can attain in static conditions. It means lowering them gradually – like through a wire – until they reach the mentioned depth. In the case described above, it would be 30 meters.

But what happens if you dive into a pool? That the watch has to sustain a sudden change of pressure that would probably exceed the stated water resistance.

Just the act of someone swimming in a pool freestyle produces a pressure on the watch of around 5 bar.

But your very own house is not secure at all. To make an example of routine real-life situations, the water faucet system of your house has a typical water pressure of 3 bar – that is, the typical pressure of around 30 meters depth. A shower would exceed that a bit – ordinarily, it is about 50 psi (pounds per square inch) – approximately 3.5 bar. Diving into a pool would subjects your watch to a pressure of at least 5 bar if not more: not something that your typical 30-meter water-resistant watch is going to withstand without consequences.

This is the reason why watchmaking companies accompany their watches with handy tables so you can check the activities you can perform while wearing your watch. Too bad that most of the time, people ignore them and instead rely on what is written on the dial, exclusively – and must have a quick consult with their watchmaker afterward.

You can find much more about horology and its fascinating history in The Watch Manual. It is a thorough e-book that explains all the basics about watchmaking and its protagonists.

To download a FREE 8-chapter extract from The Watch Manual

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