Rolling in the deep

Alex Doak

A handsome new diving watch has an ingeniously simple mechanical system to tell you your depth

Any serious digital diving watch will be able to tell you your depth as well as the time, and a host of other indications. Doing so in a mechanical watch, however, can be a complicated business. For instance, back in 1999, IWC launched the Deep One, containing a circular “Bourdon tube”, which straightened out as water entered one end of it, moving a geared hand on the dial to indicate your diving depth up to 45 metres.

Then in 2007 Jaeger-LeCoultre welded a massive chamber to the side of a diving watch case, housing a steel membrane that expanded or contracted according to the aquatic pressure. A complicated transmission system meant you could read this dialside. Four years later, the huge X-Fathoms from Blancpain employed an amorphous metal that deformed under pressure, connected to asymmetric gearing that corrected its non-linear behavior, presenting a (fairly) accurate depth reading. Got that? Phew.

And this year: a watch with a hole in it. This hardly sounds sensible for a gadget designed to go underwater, but it could be the most elegant, forehead-slappingly obvious solution to a problem watchmakers have been over-engineering for years.

Admittedly, it has taken Oris two years to get right, but the result both impressive and rather more affordable than those progenitors.

In fact, compared to those earlier efforts, Oris’s Aquis Depth Gauge is like a free diver plunging past scuba divers and their gast tanks armed with nothing more than a couple of lungfuls of air and a serene state of mind. Its engineering is brilliantly simple: it features a double-thick sapphire crystal (the “glass” cover over the dial) with a channel of air carved into its circumference – your horological“lung”, if you like. As you’ll remember from GCSE physics, “Boyle’s Law” states that pressure is inversely proportionate to volume. So, the deeper you go, the more the air in the channel is compressed by water entering its access hole at 12 o’clock. Consequently, the dark-grey/light-grey, water/air interface is gradually moved anticlockwise, its border acting as the depth indicator, read off from the yellow calibration running the circumference of the dial.“The principal is simple,” says Oris vice president Rolf Studer, despite wielding a presentation board stating that p1*V1=p2*V2V2=(p1/p2)*V1. “The guarantee that such a simple function will perform accurately was the hardest thing, though. We went through countless trials to perfect the dimensions of the air channel, its profile...”

Understandably, Oris has been quick to patent its efforts. But as well as the sheer precision of such an elemental set-up, what’s doubly impressive is the water resistance achieved with the Aquis Depth Gauge, despite there being an Achilles Heel deliberately milled around the glass. A “Zytel” gasket seals the gap between the air channel and the case, made from a nylon polyamide trademarked by DuPont and guaranteeing this watchdown to 500m, in alliance with a particularly hefty screwdown crown.

All of which will cost you a mere £2,100 – a bargain for something so innovative and which, like the best diving watches, will go with your jeans as well as your wetsuit.

Alex Doak is the managing editor of The Prodigal Guide.