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Reflection-free readability underwater

Absolutely free from fogging, pressure-resistant at any accessible diving depth and perfect readability from any angle underwater – these are the unbeatable advantages of our diving watches equipped with HYDRO Technology.

The principle

In a HYDRO watch case, the movement, dial and hands are held in a crystal-clear bath of fluid with the same refractive index as that of the sapphire crystal glass. As a result, light continues to penetrate the filling liquid through the sapphire crystal even from large angles of incidence. The highly obstructive effect of mirroring (total reflection) is thus eliminated.

In addition, the filling liquid is incompressible and replaces the air inside the case, which always contains moisture. This results in a number of advantages.

Filling the HYDRO watch case. The model shown here is the U50 HYDRO.
Advantage: reflection-free underwater
From practice for practice: The test set-up proves that both the U50 HYDRO (left) and the UX (EZM 2B) can be read under water without reflections from the same flat angles as other diving watches thanks to HYDRO technology, just as users are used to from a diving watch when not diving.
Advantage: reflection-free underwater

The crystal of a conventional diver’s watch will unavoidably reflect light underwater - but not a HYDRO watch. A HYDRO watch can be read from oblique angles underwater, just as it can when out of water. The reason for the characteristic mirroring effect is the total reflection on the bottom of the crystal. If the optical medium of “sapphire crystal” is succeeded by the medium of “air” (looking towards the dial), the light will only be reflected and no longer refracted from a certain angle. This prevents the light from penetrating the interface between the sapphire crystal and the air- filled space containing the hands. From this angle, the effect is similar to that of looking at a mirror. The hands are no longer visible. Replacing the air in the cavity containing the hands with a fluid which shares the same optical characteristics as the sapphire crystal glass neutralises this effect, making the watch face fully readable even at highly oblique angles.

Advantage: completely free from fogging

The absence of any air inside the case keeps our HYDRO watches completely free from fogging. Fogging only occurs in air which contains moisture; this can condense if the temperate falls below the “dew point”. Where there is no air humidity – there can be no condensation!

Advantage: pressure-resistant up to a diving depth of 5000 m

Fluids are virtually incompressible. The membrane back allows the internal pressure of the watch to adjust constantly to the external pressure. In principle, a HYDRO watch would therefore be pressure-resistant for any achievable diving depth. The pressure difference that exists in a conventional watch between the internal mounting pressure of a watch (1 bar) and the external water pressure (increase of 1 bar per 10 metres of water depth) is not even built up in a HYDRO watch. However, if diving depths of 5000 metres are exceeded, the quartz movement will be damaged by the high internal pressure of the watch. For this reason, there is a maximum diving depth up to which the watch can be guaranteed to function perfectly.

Every HYDRO watch is necessarily a quartz watch due to the oil filling, as the balance oscillation of a mechanical watch could not overcome the high damping in a liquid medium. Our HYDRO watches are always fitted with long-life lithium batteries and are certified as SINN diver's watches by an independent test centre.

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