It was in 2019 that I first strapped on a Reservoir Hydrosphere watch — a prototype that got me really excited to review the final retail model. Over a year later, Reservoir finally started to ship the long-awaited diver’s style watches from the French timepiece brand whose entire theme is currently retrograde minutes: jumping hour watches based on a proprietary movement module the company developed. The Hydrosphere is the still new brand’s first serious diver’s watch in both looks and performance. It’s been really cool to wear and it was totally worth the wait. For myself and other diver-style watch enthusiasts, this is easily one of the most innovative tool watches of the year.

Reservoir produces a few versions of the Hydrosphere timepiece, which vary in dial color and case material. I like the Hydrosphere Air Gauge in particular because as the name of the product implies, the dial is highly reminiscent of analog air gauges. One of the interesting things about this particular SCUBA diving instrument is that most BCD units (the vest diver’s wear which hold the air tanks) have an air gauge that looks almost identical to the watch. This means that most recreational divers today have used such air gauges and visually recognize them. Why is this important? Because the Reservoir Hydrosphere Air Gauge is one of the only luxury diving watches today that actually visually goes with today’s diving equipment. This means the watch dial is both relatable and familiar to not just watch lovers, but to a larger population of general SCUBA diving enthusiasts (like myself).

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The retrograde minutes and jumping hour dial layout that Reservoir uses is attractive but not immediately translatable to a traditional analog diver’s watch. A big part of this is the fact that the rotating timing bezel assumes the minute hand makes full rotations around the dial. In this instance, the minute hand moves along an arc that is perhaps 2/3 of the circumference of the entire dial. That means the 60-minute countdown scale needed to be reworked a bit, while an extra mental calculation needs to be done if the minute hand jumps back to the starting position. I think Reservoir overcame this challenge nicely, but it does take a bit of time to use all of the traditional diver’s watch features in a way that mainstream watch lovers understand. The rotating bezel itself has a ceramic insert, which is one of the many “premium” features that are welcome to have in what is otherwise a well-made novelty product. And I, for one, really appreciate the novelty. This is also a good opportunity to mention a similar diver’s watch I recently reviewed — which was also the first diver’s piece from a small brand — the jumping hour MeisterSinger Salthora Meta X (aBlogtoWatch review here). I think it would be interesting for anyone romanced by these “alternative divers” to see how these two similarly priced watches compare.

Living with the watch for a while, I found the legibility to be simple, even though it requires some getting used to over a traditional 12-hour dial. I really like that Reservoir included a small upside-down magnifier over the jumping hour window near 6 o’clock on the dial. This helps improve readability for the hours. Under the window is probably the most attractive linear power-reserve indicator I’ve seen on a watch in a while — just something about how it was designed makes it feel very attractive. Overall detailing on the dial and bezel are excellent. Very high marks to Reservoir on the attention to precision and details on these areas (which many smaller new brands don’t focus on as meticulously).

As a diver’s watch, the Hydrosphere is water-resistant to 250 meters and has a built-in automatic helium release valve. The case is larger at 45mm-wide, but it wears smaller due to the relatively narrow, stubby lugs. More so, since the lugs are placed toward the bottom of the case, the Hydrosphere feels like it is riding on your wrist, which enhances comfort and makes the overall size more suitable to smaller wrists. The case is also nearly 15mm-thick with the domed sapphire crystal. It doesn’t feel too thick, but this isn’t a small watch, per se. Even though the case is said to be 45mm-wide, the bezel itself is a bit wider at about 47mm in width. So again, this is a larger timepiece but one that wears a bit smaller than its bulk would suggest.

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Reservoir sells each Hydropshere in steel with both a matching metal bracelet and a bespoke rubber strap. To swap them out, you’ll need to use a screwdriver but otherwise, I applaud the company for offering both case attachment options. The reality is that if you are actually diving with the watch, the rubber strap is more practical given that it keeps the watch more secure. If you are wearing the Hydrosphere around town as a lifestyle watch (which I think will be mostly where this — like other dive watches — will end up), then the bracelet offers a slightly more sophisticated, high-end feel.

The bracelet is nicely made, and even though it has a generic three-link design to it, you can tell by the details such as the slightly curved links that this is not a generic bracelet. Further, the deployant clasp has a micro-adjust feature that can easily come in handy to expand the bracelet size on the spot. The micro-adjust system is extremely efficient but visually seems a bit more basic than what we can find in some other luxury diver’s watches such as Rolex or Omega.

Reservoir designed a rather conservative caseback for the Hydrosphere — which I think is a bit of a missed opportunity. No, I don’t want some cheesy engraving of a diver, but certain themed visuals or a view of the movement could have been nice to help add flavor this otherwise tasty horological dish. Speaking of visuals, this Air Gauge version of the Hydrosphere has an entirely lume-painted dial. The lume isn’t super-thickly applied, but there is a lot of it over the dial. Unfortunately, the numerals in the jumping hour window are not lume-painted. So, while the darkness effect for the Hydrosphere Air Gauge is cool-looking, it is marred by some minor practicality issues that I have a feeling the Reservoir brand will remedy in future diver’s watch models since these products are too good to not continue long into the future.

Powering the watch is a base Swiss Made ETA 2824-2 automatic movement which has a specially made module system placed over it. The module system was developed by Reservoir and includes the power reserve, jumping hour, and retrograde seconds functionality. The watch does indeed have a seconds hands, which is the small centrally mounted disc in the middle of the dial. This operates more as a “running indicator” but can be used if you need a seconds counter. The movement with the module naturally has slightly less power reserve than without it given the increased power-consumption demands. With the 124-component module, the automatic movement operates at 4Hz with a 37-hour power reserve. Having the power-reserve indicator on the dial makes things very handy.

I am overall really happy with the Reservoir Hydrosphere Air Gauge, both as a luxury novelty wearable and as a tool watch. Reservoir did the challenging task of making both a functional timepiece as well as an emotionally charged wearable that needs to be more than just a practical tool on the wrist. Price-wise, the Hydrosphere isn’t exactly entry-level, but it feels fair given what else you can get for the price — as well as what other decently made jumping hour, retrograde second watches are out there. I fully anticipate these watches become increasingly interesting to members of the timepiece collector community who are constantly seeking novelty in a product that also wears and feels familiar. Price for Reservoir Hydrosphere Air Gauge reference RSV03.HY/130-21.AG watch is $4,300 USD. Learn more at the Reservoir website here.

Necessary Data
>Brand: Reservoir
>Model: Hydrosphere Air Gauge reference RSV03.HY/130-21.AG
>Price: $4,300 USD
>Size: 45mm-wide, ~15mm-thick, and ~52mm lug-to-lug distance.
>When reviewer would personally wear it: Nice alternative daily dive-style watch when you want to stand out just a little bit. Will look familiar to those who are experienced divers.
>Friend we’d recommend it to first: Watch lover interested in diver-style watches and jumping hour complications that wants a particularly well-done “themed” watch from a newer brand.
>Best characteristic of watch: Excellent originality and expression of the air gauge theme. Makes a cool tool watch that is legible but distinctive when it comes to market choices. Price feels fair and detailing throughout is overall very good.
>Worst characteristic of watch: Case size might be too large for some wrists. Caseback is a bit simple. Jumping hour numerals not lumed.

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