Monochrome Watches
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Reservoir Hydrosphere “Air Gauge” – A Very Unique Dive Watch

Inspired by old diving manometers, the Air Gauge features a unique display with loads of cool features.

| By Brice Goulard | 8 min read |
Reservoir Hydrosphere Air Gauge Dive Watch

I know many people complain about dive watches. Not because of what they are intrinsically, but because many of them look the same (the Submariner-like market is huge…) Yet, there’s a very good reason for this: a norm, the ISO 6425 standard, regulates the concept of a dive watch. However, some watchmakers have decided to think outside the box and to offer cool, original and unique watches to divers (and occasional sportsmen). Like for instance the De Bethune DB28GS we told you about this morning. Another one, which is certainly one of the most striking examples of thinking outside the Sub-look-a-like-box comes from France. Let’s take a closer look at the Reservoir Hydrosphere “Air Gauge”, a watch that combines diving capacities, mechanical beauty and cool design.

Reservoir Hydrosphere Air Gauge Dive Watch


Reservoir (the French word for “fuel tank”) is a young brand. As suggested by its name, the first design was born from the founder’s passion for measurement instruments (for the display) and old jerrycans (for some of the case elements). In terms of watchmaking, this translated into a gauge-like display based on a proprietary module to indicate the time with jumping hours and retrograde minutes.

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The first Reservoir watches were classic car-inspired models. The collection also comprises aviation-themed watches, with this same original display. As the brand grows, the team at Reservoir has decided to create a unique dive watch – which is clever considering the display, where the minute hand occupies centre stage (and we know that the main indication when diving are minutes).

The main source of inspiration for the Reservoir Hydrosphere, an old pressure-gauge (manometer)

As a diving instrument, the new Reservoir Hydrosphere collection couldn’t rely on automotive gauges anymore. Yet, divers also use measuring instruments when plunging, including a manometer (like the one shown above). This instrument, a crucial piece of equipment when diving (indicating the pressure of the gas in the bottle), also relies on a “gauge-like” display and was the perfect starting point to create a Reservoir dive watch. Side by side, the resemblance between the manometer (above) and the dial of the Hydrosphere is undeniable (especially in the white dial model we had for this review).

Case and design

The case of the Reservoir Hydrosphere is an interesting mix between classic dive watch features and Reservoir’s DNA. The watch is a solid piece of equipment with a stainless steel container and respectable dimensions – 45mm diameter, which as we’ll explain later isn’t that important.

Reservoir Hydrosphere Air Gauge Dive Watch

The Reservoir Hydrosphere is built around a circular container fashioned out of 316L stainless steel, entirely brushed for a more robust look. On top is a domed sapphire crystal (which has an effective anti-reflective coating) surrounded by a deeply notched steel bezel, which is easy to operate with gloves. The bezel features a black ceramic insert, again entirely brushed, with clear inscriptions that are luminescent in the dark.

Reservoir Hydrosphere Air Gauge Dive Watch

At 3 o’clock, the crown, which is screwed for water-resistance, is coated with rubber – again, for easy manipulation with gloves or when the watch is wet. At 9 o’clock, integrated into the caseband is a discreet helium escape valve. The caseback is plain steel and secured by four screws resulting in a comfortable water-resistance of 250 metres / 25 bars. Overall the watch is nicely designed and well-executed, with neat adjustments of the parts and pleasant surface finishing.

Reservoir Hydrosphere Air Gauge Dive Watch

As we mentioned, the diameter is 45mm, which is admittedly large. However, the shape of the case and the way the bracelet or the rubber strap are attached to it is rather special. As you’ve noticed, the Reservoir Hydrosphere has no lugs and the bracelet is attached directly to the caseback. This means that the lug-to-lug measurement is also 45mm, far less than most of the 42mm watches on the market. As a result, the watch is compact and perfectly balanced on the wrist. Certainly, it isn’t a small watch but one that feels much smaller than you’d expect. See how it looks on my small 16.5cm wrist.

Reservoir Hydrosphere Air Gauge Dive Watch

Dial and display

Most of the originality of the Reservoir Hydrosphere comes from its dial. Three versions are available: a blue dial with the “Blue Hole” model; a black dial with the “Blackfin” model; and finally, there’s this white dial version, named “Air Gauge”, which the most appealing of the lot – both in daytime and nighttime (more on that in a few).

Reservoir Hydrosphere Air Gauge Dive Watch

The main point of interest with watches made by Reservoir is their display. On the contrary to most of the dive watches that rely on three central hands, the Hydrosphere benefits from the brand’s proprietary module to offer a display that is both original, mechanically interesting and quite relevant in a diver’s context. As we mentioned, when it comes to diving measurements, the minute hand is key.

Reservoir Hydrosphere Air Gauge Dive Watch

This is how the Reservoir Hydrosphere splits its four indications:

  • The large retrograde minute hand, which runs from 00 to 60 on a 240-degree arch, is centrally mounted. Unconventional for sure, this minute hand needs a (short) period of adaptation but once you get used to it, it becomes both intuitive and extremely legible
  • The jumping hour is in a window at 6 o’clock, precisely changing indication when the minute hand jumps back to the 00 position. In order to increase legibility, the hour window has here been placed under a magnifier
  • Just below the jumping hours is the power reserve indicator, a reminder of the initial inspiration behind the brand
  • New to this model is a centrally mounted running indication (basically a small disc running the seconds), something necessary in dive watches to be sure the watch is still running.

As for the design of the dial itself, the resemblance with old manometers is rather obvious, with the use of a striped red zone from 00 to 10 and a specific style for the minute track. Large applied numerals and a highly contrasting black minute hand allow for a quick consultation of the time. Same goes for nighttime legibility… Which is also when the Reservoir Hydrosphere “Air Gauge” is at its coolest.

Reservoir Hydrosphere Air Gauge Dive Watch

The main specificity of this white version, as opposed to the black and blue models, is its luminescent dial where all the indications are left black. Not only is the legibility superb but the result is simply stunning. How cool is that fully luminous dial?

How to operate the bezel?

Now comes the tricky part… Having a retrograde hand for the minutes operating on a 240-degree arch and a rotating bezel on a 360-degree scale is obviously not convenient – if not totally unnecessary. For this reason, the brand had to develop a new bezel for its Reservoir Hydrosphere, which features two scales.

Reservoir Hydrosphere Air Gauge Dive Watch

From 00 to 45, this unique architecture isn’t problematic. Simply position the triangle in front of the minute hand and read the scale on the bezel, just like any other dive watch. However, when the minute hand is positioned between 45 and 60, this means that it will jump back to the 00 position before your 15-minute scale is over. The idea Reservoir came up with is simple but efficient, as explained below:

Step 1, position the triangle in front of the minute hand, like this (here at 55):

Reservoir Hydrosphere Air Gauge Dive Watch

Then, once the minute hand jumps back to zero, a second track (marked “use after 45 minutes” on the bezel) takes over and follows up the counting session. See below, once the minute hand is back to 05, with the right timing indications on the bezel.

Reservoir Hydrosphere Air Gauge Dive Watch

This trick, a necessity considering the specific display of the Reservoir Hydrosphere “Air Gauge”, is certainly less intuitive than a classic dive watch. However, once you’re used to operating the bezel it becomes more natural.


Powering the display of the Reservoir Hydrosphere is a double-decker movement. The timekeeping part – meaning storage of energy, the transmission of energy and control of the movement’s rate – is controlled by a reliable, tested and proven calibre ETA-2824. Its function is mainly to provide energy and accuracy to the display. As always, it runs at 4Hz and stores up to 37 hours of energy (the display used here requires more energy than traditional hands).

Reservoir Watches - review

On top of the movement is a proprietary module, developed by Télôs, a movement design/production company, specialized in complications and unique displays. This 124-part module is in charge of the display. A series of gears and springs let the hour disc jump precisely every 60 minutes. A spring is gradually charged during an hour and released precisely when the hour hand reaches the 60-minute position. This module is as complex as the movement itself and comprises almost as many parts as the base movement. It represents most of the added-value of this watch.


As mentioned, the Reservoir Hydrosphere features a specific construction when it comes to the bracelet attachments. The links are screwed directly on the caseback (see photo above), allowing for a compact architecture and a smaller watch on the wrist.

Reservoir Hydrosphere Air Gauge Dive Watch

The watch is delivered with two options. First is a classic 3-link, fully brushed stainless steel bracelet with folding buckle and easy diving extension – which can serve as micro-adjustment too. The steel bracelet is well executed and comfortable.

Reservoir Hydrosphere Air Gauge Dive Watch

Also included in the package is a rubber strap with a steel pin buckle. It can be easily attached with a small screwdriver. The main advantage of this rubber strap is to make the watch even more compact and lighter. It is soft and made of high-quality material.


I’ve been pleasantly surprised by the Reservoir Hydrosphere “Air Gauge”. Certainly, it won’t talk to the masses and is a niche product. Still, it is a unique and mechanically advanced display, the original design (without being too extreme), the cleverness of the bezel (even though unconventional), the cool features (the manometer inspiration, the full luminous dial) and the overall quality of the execution have convinced me.

Price and availability

The white-dial Reservoir Hydrosphere “Air Gauge” and its black and blue siblings are now available at retailers and on the brand’s webshop. It is priced at EUR 4,250 or USD 4,300. More details at

9 responses

  1. My only problem with this otherwise supercool watch is that the hour disk is BLACK exactly when I want to look at it — taking it off the nightstand in the middle of the night. HUGE MISTAKE on an otherwise amazing watch and makes it a NO BUY from me.

  2. Definitely not one I’d buy per se, but it will surely cause some conversations for those who do!

  3. My first thoughts were a little dismissive but after reading this review and seeing how clear, useful and clever this is, I am very taken with it. I was expecting an insane price but frankly, I think this is (just) reasonable.
    Excellent work guys.

  4. Great review! I loved the driving and pilot ones, but didn’t understand or appreciate this model until now.

  5. As a professional diver, this would not be a great choice in the water as it looks too much like the air pressure gauge. No reason for that, and the bezel markings are way to small to be visible in turbid water.
    For a desk diver or conversation piece though, I like it!

  6. Surprisingly easy to use and very beautiful watch/bracelet. In the lume shot it seems the black hour number is not visible making it useless at night though.

  7. The only problem is, even if all the hours were made of 100% luminescent material, they would lie hidden from ambient light until it was their turn to be shown, so by the time you turned the light off, you’d only have the remainder of the hour to read it.
    Hhhmmmm. Don’t know if there’s a fix for this one.

  8. A nice piece for one that collects super cool watches. Hard to see how this can be seen on any wrist that does not belong to a diver in action

  9. Like it a lot, great pictures of the watch. But once the rubber strap goes, replacement options will be limited. Looks like a proprietary solution.

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