Dive watches compared

The ISO 6425 standard defines what a watch must meet to count as a dive watch. This includes water resistance of at least 100 metres (200 m or 20 bar is common), a unidirectional rotating bezel for timing dives, good legibility in total darkness, resistance to salt water and shocks, and a secure strap attachment. Every single watch is tested. Watches marked "Diver's" with a reference to the standard are genuine dive watches; many models with diver styling, by contrast, don't officially meet the standard.

For swimming, snorkelling and seaside holidays that isn't necessary either. A well-made watch with 10 bar or more and a screw-down crown is enough here.

The unidirectional bezel can only be turned anticlockwise. If it gets knocked by accident, it shows a longer rather than a shorter dive time – a safety principle. A screw-down crown seals the case further; you have to screw it back down before it comes into contact with water. Luminous material such as Super-LumiNova (grades C3 or BGW9) ensures legibility in the dark.

The figure in metres is a static test pressure under lab conditions, not a permitted diving depth. Movement in water, temperature changes and ageing seals change the load. So: 10 bar is designed for swimming and snorkelling; for scuba diving it should be a dive watch to ISO 6425 – and if in doubt, a dive computer complements the watch. If you use the watch in water regularly, have a watchmaker check its water resistance about once a year, especially after a battery change.

After swimming in the sea or in chlorinated water, rinse the watch with clean fresh water and turn the bezel as you do so, so that no salt builds up.