The caliber 400, on the other hand, has two barrels and is an automatic caliber, designed for maximum efficiency and longevity. The watch has a five day power reserve and, remarkably, the recommended service interval is ten years.

The idea was to create what in watchmaking is called a tracteur – a simple, strong movement, in a size allowing it to be used in a range of different timepieces, which would offer a real technical step up from the supplied movements in many Oris watches. The use of supplied calibers is a big part of what keeps Oris affordable, but the new caliber 400 offers not just in-house bragging rights, but also well-thought-through engineering, and major benefits to the owner of any watch using it – for instance, the Aquis diver’s watches.

The sub-$4,000 dive watch world is full of hot competition right now, but if you’re looking for a watch with a movement as no-nonsense as a dive-watch caliber should be, you’ll want to put the Aquis on your list.

If you’re wondering where you start when you start designing a movement from scratch, the answer is: Size matters. The dimensions of the movement are what determine how wide a range of watches you can use it in, and you can’t start finalizing other aspects of the caliber until the size question is settled.

“The dimensions are extremely important,” says Oris COO Beat Fischli. “If you have not fixed the dimensions on the level of construction, you must have this definition before you begin. And our caliber has a diameter of 30 millimeters. We made it bigger than [the Sellita caliber] SW-200, for example. And this shows clearly that we did not just make something that’s compatible with the Sellita movement. And so we know before we started, we knew that we can perfectly house it with perfect proportions, down to cases 38mm in diameter.”

One of the targets for the engineers and watchmakers working on the movement was to give it better-than-average resistance to magnetism. Antimagnetic materials are important – the caliber 400 has a silicon lever and balance wheel, but it does not use a silicon balance spring. Despite this, the movement showed a deviation of less than 10 seconds per day after exposure to a 2550 gauss magnetic field. The international standard for “antimagnetic” watches, ISO 764, specifies a 30 second per day deviation, after exposure to a 200 gauss field.

Fischli explains that in addition to materials, the physical configuration of the movement can have a surprisingly large effect on the degree to which it resists magnetism.

“Sometimes we’ve been surprised, sometimes very confirmed in what we have been expecting. Magnetism, the characteristics, how a caliber behaves in the magnetic fields and above all, after exposure to magnetic fields, it begins even before the choice of the materials. It’s already very much influenced by the general layout, the design of the caliber. How many layers do you have? Which wheels? The whole construction itself. It’s incredible, but the impact is huge. We’ve done comparison tests with caliber 400 with this layout in early stages, compared to standard movements from ETA and Sellita, and that was the first important and also a little bit surprising point we found out there.”

One of the biggest points of wear in any automatic movement is the winding system – specifically, the bearings for the winding rotor, which is in constant motion and which produces some of the biggest mechanical loads in the watch. Another common point of wear and eventual mechanical failure are the reverser systems, which are necessary in movements that wind in both directions. To reduce parts count, and improve reliability, Oris went for a system that winds in one direction (no reversers) and also eliminated the usual ball bearings, in favor of a sleeve-and-clip attachment (no ball bearings).

“And the winding system,” Fischli says. “We have years and years and years of experience also in after sales. That’s one of the key points or key issues we see when watches with automatic movements come in for servicing … one of the most frequent problems has exactly just to do with the winding system, with a ball bearing and with this reversing system by the direction of the rotating oscillating weight. Following our strategy, we made it simpler than that. We just left off these kinds of parts. We used the unidirectional rotating oscillator, so no reversing system needed. And we also left off the ball bearing and we implemented a sleeve bearing.”

Fischli explains that part of the secret to the long power reserve, and to the long service interval, is simply engineering the movement for maximum efficiency. The two mainspring barrels, in contrast to the beast at the heart of the caliber 110, deliver relatively low torque. “There are sequential, these two barrels, which gives a very long mainspring,” Fischli says. “And then what we did here, we really, I would say dramatically reduced whatever force is released in this movement. The torque provided by this mainspring is extremely low.”

Every element in the going train, including the profiles of the gear teeth, to the low-inertial escapement components, is an aid to efficiency. “From the mainsprings to the hands at the end is 85%. On a standard movement, normally you are around 70% of efficiency ratio,” Fischli explains.

The caliber 400 is deceptively simple. In a watchmaking world where a high parts count is often something for the marketing department to brag about, the caliber 400 has gone in the opposite direction. It’s a reminder that good engineering generally keeps the number of parts you need to the necessary minimum.

This sort of thing is real watchmaking and the caliber 400 is, especially in a watch like the Aquis Date, which retails for $3,500 on a bracelet, an extraordinary piece of added value for anyone who wants their sports watch to be as tough and reliable as it looks.

All photos, Tiffany Wade. For full specs and pricing for the Aquis Date, check out James Stacey’s Introducing post.

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