Water resistance

Water resistance is not a binary characteristic: it's a system of multiple components that must work together, and it takes just one to fail for everything else to become worthless. I say this after decades spent disassembling watches that arrived at my bench with infiltrations that no one should have expected, yet there they were.

The most vulnerable sealing point is almost always the crown. The screw-down crown solves the problem by threading into the case tube and creating a hermetic seal. Before the 1970s it was a rare feature, almost a luxury. Today it's the standard on any watch claiming more than 100 meters. Some manufacturers add a visible colored ring when the crown is unscrewed: it's a visual reminder, functional and not decorative, to remember to close it before water exposure. A trivial detail, but damage avoided.

Certifications add a layer of external control. The ISO 6425 standard defines minimum requirements for a true diving watch: static and dynamic resistance, readability, unidirectional bezel. The German DIN 8310 standard is equally rigorous. Claiming 500 meters without testing to recognized protocols means nothing.

There are less common but technically interesting construction solutions. The monoblock case, carved from a single steel block with movement access from the front, virtually eliminates the risk of infiltration from the caseback: it's the logical choice for saturation diving watches. An oil-filled, silicone, or low-viscosity fluorinated case aligns the refractive index with the sapphire crystal, improves readability at depth and reinforces sealing, but requires a thermal compensation system because the oil expands. EPSA's Super Compressor, developed in the 1950s, instead used an undulating spring caseback that compressed as external pressure increased, adapting the seal to depth without the diver's intervention.

Materials matter as much as construction. Titanium resists saltwater corrosion better than stainless steel because of the oxide film that forms naturally on its surface. Ceramic on bezels doesn't oxidize, doesn't lose color, doesn't require the attention that exposed steel would need in a marine environment. Chronograph case openings, by contrast, are structurally incompatible with diving: this is why dive chronographs require special construction solutions and remain complex objects to design.

The skin diver occupies a separate category: resistance between 10 and 20 atmospheres, curved case, large unprotected crown, contained diameter. It's not a professional diving watch, but it's designed to stay in water without fuss.