Deep within Rolex’s landmark Geneva HQ is a 1.3 tonne lump of stainless steel. Somewhat unprepossessing from the outside, inside is a hostile microcosm.

The tank simulates pressure at 16,000ft below sea level and it is inside that Rolex’s Deepsea watches are tested before release onto the market.


From deep sea diving to your morning shower

It is, potentially, an expensive process. The smallest flaw in each watch’s construction will make it explode, so it pays to make sure everything is right before undergoing this hyperbaric assault.

But this also means that the company has, for decades, been able to supply specialist pieces for divers working for the likes of Comex, the underwater engineering firm whose elite members hold the world record for the deepest saturation dives.

Rolex can also claim credibility for the wearer whose depths rarely surpass that of his morning shower. In fact, each Rolex is tested to a depth 25% greater than that stated on the dial.

And that’s by no means the only test a watch might go through. Rolex, for instance, puts its Oysterlock bracelets through 26 different kinds of drop tests; the fastening is opened and closed tens of thousands of times; it’s immersed in salt and sandy water and in chlorine solutions.


Taking testing to the extreme

“Shock, acidity, temperature, magnetism, legibility… all the variables that might affect a watch’s performance have to be tested for,” says Jean-Paul Girardin, vice president of Breitling. “These tests have to comply with regulations local and global, because our customers travel.”

“The more extreme the conditions a watch has to operate in, the more extreme testing has to be. We tested our Emergency watch to minus 20 degrees Celsius (minus four degress Fahrenheit), for example – that would freeze the oils in any normal watch. There was no test at all for the transmitter batteries we developed for the same piece, so you end up establishing your own standard. You need a lot of skills outside of watchmaking: mathematicians, physicists, chemists…”


Life is crude

And, occasionally, a big steel hammer to hit your watch with, over and over. Dubbed the ‘sheep’s foot test’ by those in the business, this is one of the oldest but still most important of trials for many Swiss timepieces.

“It’s a very crude test. People think you’re kidding when they see it: ‘what, you’re going to whack that very expensive watch?’,” says Theodore Diehl,