Watch bezel: what it is and how does it work.

The watch's rotating bezel is an essential component on diving watches and is used to compute diving times accurately. Divers use it as a means to make sure the time they spend underwater is in line with their estimation.

The bezel is instrumental in computing decompression times and measuring the total time elapsed while underwater. When deep diving, you can't surface too rapidly; given the human body is subject to continuously changing pressures, inert gases like nitrogen might pervade blood and body tissues. Our body, which needs to adapt to normal atmospheric pressure progressively, naturally expels these gases. If a diver is not abiding by precise rules, he or she might expose to the so-called decompression sickness, the outcome being severe brain damage due to nitrogen spreading across the brain.

Decompression times' computation considers several factors, including the maximum depth and dive time, to cite a few. The decompression stops require any diver to apply rules set in a specific table, representing a reference guide to any expert diver. Pictured above is the Mido Decompression Timer, showcasing reference decompressione times, in feet and meters, on the dial.

How a watch bezel works

A watch bezel includes a sexagesimal scale, and its functionality is not anything different from a standard timer. When diving, please align the minute hand to the zero markers engraved on the bezel. The bezel's ring usually advances one step or click at a time; that step marks a minute and makes it easier to adjust it precisely. Make it too smooth, and you'll end up inaccurately set your dive time.

Watch bezel: the main features.

Given its specific function, the ring's design is such to make it easy to use while diving:

Unidirectional rotation: the bezel rotates counterclockwise only. By doing so, you minimize the risk it is inadvertently maneuvered and set dive times higher than predicted. This safety feature ensures you won't dive more than you'll expect, considering the limited oxygen tank's capacity.

Grooving: each bezel comes standard with grooves to allow a diver to grab it with gloves. Any pro diver usually operates under strict conditions, where reduced visibility requires him to grip it easily. The grooves on the bezel's side make sure the surface is not too slippery.

Good readability: Underwater, visibility is often lacking, even more so when you're deep-diving where sunlight is fading. Here is why a diving watch's bezel intensely glows in the dark; luminescent material is essential to make a diving watch glow in the dark and ensure dive time is readable at a glance.

How to replace the watch bezel

Be aware that an expert watchmaker is the right person to service your watch, even more so if you own a luxury diving watch. Although most diving watches share a standard design, getting your hands on yours by yourself might irreversibly damage your timepiece.

With that said, here is a best practice among amateur watch repairers; bezels are locked into the case, you usually need to use a small tool as a pry bar. The primary step is to place a very slim tool, like a cutter, in the small gap between the case and bezel and use it as a pry bar, then. To avoid damaging the case, make sure you place a smooth material between the case and the bezel, both sides of the cutter. Please apply an adhesive band or an equally thin piece of paper to avoid scratching your timepiece. When operating, please be careful not to lose the small spring and stud placed at six under the bezel; they ensure the bezel can rotate counterclockwise. To sum things up:

• Get a thin and robust tool, like a cutter

• Cover it with adhesive tape or paper to avoid scratching your watch and harm yourself

• Carefully place it into the gap between the bezel and the watch case, and smoothly use it as a pry bar

• Be careful not to lose the small parts placed under the bezel, ensuring proper operation

• Apply the new bezel and lock it with a light pressure

As we have already said, this is just a common practice you can't adapt to all watches; you'd better treat your watch with a professional watch repairer.

Watch bezel: types and models.

The bezel is as functional as it complements your watch's style. The former comes with various designs, different kinds of numerals, color palettes, and materials.

There are aluminum rings, as with the Seiko Prospex SPB183J1 or in ceramic, like the Rado Captain Cook 300 meters. Sapphire-made bezels deserve first-page news since they are as refined as hard to find today. The most significant example is the Blancpain Fifty Fathoms, the timepiece priding itself with being the first diving watch in history. Not only do most bezel designs differ from each other in terms of styles, colors, and materials they adopt, their placement on a timepiece may also vary from watch to watch.

Case in point, the Longines Legend Diver Watch 2020-2021 adopts an internal rotating ring, operated by a second crown, instead of an external two-piece rotating bezel.

(Photo credit: Peter Tung and Marco Antinori for Horbiter®)

Tommaso Sabia @Horbiter®