It’s no exaggeration to say that a deep-sea diver’s survival is intimately linked to the reliability of their watch. Under water, a watch becomes so much more than a tool to tell the time, recording the length of time you’ve been submerged and, with some models, indicating how much air is left in the tank.

To qualify as a dive watch, it must have a water resistance of at least 100 metres, but most average 300 metres. It goes without saying, durability and legibility are equally important.

Elegant with its “Méga Tapisserie” dial, the Audemars Piguet Royal Oak Offshore Diver is well equipped for aquatic sports, with water resistance of 300 metres and a luminescent coating.

Cartier, meanwhile, impresses with the Calibre de Cartier Diver, which is ISO-certified as meeting strict standards for eight criteria: unidirectional bezel, legibility, visibility in the dark, running indication, magnetic resistance, shock resistance, chemical resistance, strap durability, and water and pressure resistance.

Omega’s Seamaster Planet Ocean Auto has an innovative bezel that combines ceramic and rubber—an industry first. Its numbers and scales are rendered in Liquidmetal to ensure legibility, and the watch is water resistant to 600 metres.

When film director James Cameron embarked in 2012 on his solo expedition to the floor of the 11,000-metre-deep Mariana Trench, attached to the arm of his submersible was an experimental divers watch, the Rolex Deepsea Challenge. Based on this now iconic watch, Rolex created the Deepsea Sea-Dweller.

While it doesn’t come close to the water resistance of Cameron’s trusty companion, the Deepsea Sea-Dweller can withstand a depth of 3,900 metres. While very few will go on such extreme diving expeditions, it’s good to know this piece exists should opportunity knock and nerves permit.

This article was originally published in Hong Kong Tatler's July 2016 issue