Boyle’s Law states that as the volume of a gas decreases, its pressure increases. PV = k. Pretty simple stuff, even to my nitrogen-addled brain as I coasted over the edge of the reef and checked my depth, which read a shade over 25 meters. Frankly, I hated science in school, but if the experiments we did back then had involved scuba diving in the Caribbean with a Swiss watch on my wrist, I might have opted to major in Physics instead of English Literature. The watch I was wearing on this dive, the ORIS Aquis Depth Gauge, aside from its chunky-handsome looks and colorful dial, is a perfect example of Boyle’s Law at work, a principle I was testing on every dive during a recent week in Bonaire.

ORIS has always been a favorite of real dive watch fans, thanks to the classic diver looks, solid build quality, and affordable prices. But last year, ORIS debuted the Aquis Depth Gauge, which ratchets up the usefulness of the watch for actual diving, thanks to an integrated mechanical depth gauge. As we discussed a few weeks ago, depth gauge watches typically make use of some sort of pressure membrane or Bourdon tube mechanism and mechanical needle to indicate depth, but the Aquis Depth Gauge uses water itself as the gauge. Defying convention, the watch has an orifice in the sapphire crystal that lets water enter a channel around its circumference. As the water pressure increases at depth, the air inside the channel gets compressed and the line where air and water meet shows the depth against a scale printed on the dial below. It is a very elegant solution with no moving parts. But how well does it work? I wanted to find out.

The Aquis Depth Gauge takes its design cues from the rest of ORIS’s Aquis line-up of divers, which is more classic and less busy than the top shelf ProDiver watches that have a finicky locking bezel mechanism. The case is 46 millimeters, which is big even by today’s standards, but fine for all but the smallest wrists thanks to short lugs. It fits with a distinct instrument vibe that works with the depth gauge function. Still, rendered in stainless steel, this is a very heavy watch, even on the rubber strap. 

Forgetting about the unique depth gauge functionality for a moment, for $3,500, the Aquis is a well-made, full-featured watch for the price. The engraved and painted ceramic bezel is particularly nice, made even more so by its matte finish. Bezel action is tight and precise and I’ll resort to dive watch review cliche and say, yes, it is grippy even with wet or gloved hands. Crown action is equally good and the Selitta SW 200 movement’s timekeeping seemed adequately accurate over the week of wearing it in active conditions. But you didn’t come here to read about the bezel or the crown. It’s the depth gauge function that makes this watch interesting. 

The depth gauge starts working in as little as a few feet of water. The depth scale goes from 1 to 100 meters around the dial and is calibrated to take Boyle’s Law into account. This is reflected by the fact that for the first 10 meters, the spacing between markings is wide due to the shallow depth and relatively low water pressure. From there, the spacing gets narrower and the increments jump to 4, 5, then 10, and finally 20 meters difference between them, reflecting the building water pressure (at 10 meters, you already add a full atmosphere of pressure). The scale goes up to 100 meters though few divers will ever see that depth and beyond 30 meters (100 feet), the lack of precision means the watch ceases to be a useful reference.

I spent most of my dives between 10 and 20 meters, where the gauge was useful and the depth readings were legible. The water in the tube shows a dark gray while the compressed air pressure is light, almost white (the sapphire behind). Digital depth readings and those indicated with a needle or marker are clearer but once I knew what to look for, the ORIS was a cinch to read. The watch is calibrated in meters of depth, which for those of us (Americans, basically) who still use feet as a unit of measure, it takes some quick math. Comparing the Aquis to my digital Suunto dive computer (set to feet) wasn’t an exact science, but the depth gauge proved to be remarkably accurate, from shallow to deep depths. 

After wearing the ORIS Aquis Depth Gauge for a week, it quickly became a faithful companion, a conversation starter and a useful and fun tool while diving. Whether or not it will be popular among non-divers remains questionable since its functionality is lost on terra firma and a watch with a hole in its crystal isn’t as practical for day to day wear. Still for “desk divers” there are other Aquis dive watches to choose from, those that don’t require any knowledge of physics at all. Class dismissed.

BRAND: Oris

MODEL: Depth Gauge

MOVEMENT: Swiss Automatic