In this article in our series on the basics of divers' watches, we take on what is probably the most distinctive element of a dip watch: the rotating bezel.

Its function is really rather easy: before a diver's descent, the 12 o'clock bezel mark is aligned with all the minute hand, permitting the elapsed time, around 60 minutes, to be read on the bezel (which is why quite a couple of dive watches include a particularly prominent second hand). A unidirectional, ratcheting structure ensures -- when the bezel is inadvertently moved -- that the time spent underwater would be signaled as longer than really spent, giving the diver with a safety reserve for his now more impending ascent. The bezel/minute hand combination doesn't, but directly quantify how much air stays in the air tank, as still can be read quite often in media releases.

A standard scuba dive (where the diver is equipped with a standard air tank) generally lasts 30 to 50 minutes, largely depending on the depth reached and the form the diver is in (basically, how physically demanding the dive is). This explains why the first 15 to 20 minutes on the bezel inlay tend to be more highlighted -- the end of the sector theoretically signifies the purpose of recurrence (exclusion: "countdown" bezels that mark the period of ascent). In order to properly time decompression stops at the end of a dip, central-minutes chronographs like the Aquastar Benthos or even split-minute chronographs, such as the IWC Aquatimer Chronograph from 2004, supply an interesting complication (if the diver not use a pc).

But, back to the start of a dive: In reality, the bezel is adapting while the diver is geared up and ready to start the dip -- which is, the majority of the time, when he's already in the water or onto a boat before entering the water. It is rarely done in a sterile living area, wearing no gloves, even when one can take the watch off to set its bezel. So, despite how much I personally love the Omega Ploprof (that comes with a bi-directional external bezel using a locking mechanism) and the Hublot Oceanographic 4000 (whose unidirectional internal bezel is controlled via a screw-down crown that's then put behind a protective cap), neither are among the simplest watches to be operated single-handedly when worn in the water. And I would strongly advise you never to remove a wet luxury watch from your wrist whenever there's a bottomless pit below you.

From a building point-of-view, there are two main approaches:

1. External bezel
First used for a dive watch by Rolex and Blancpain (inspired by earlier pilots' watches) in 1953/54, this remains the easiest and most user-friendly strategy. Disadvantages include wear from sand, debris or salt getting between the case and the bezel, and also the possibility of inadvertently moving or damaging the bezel.

As a solution to these problems, Citizen introduced a removable bezel with the Citizen Promaster 1000 in 2002, also IWC established the Ocean 2000 in 1984, with a bezel that may only be worked counter-clockwise when pushed down (a notion re-introduced in 1998 using its GST Aquatimer). This concept was similarly executed earlier by Certina, using its DS-2 500m in 1968, and afterwards in 2003 by TAG Heuer for the Aquagraph 2000 Chronograph (with a two component bezel) and by Oris in 2009 with the Oris Prodiver (whose bezel needed to be lifted). More or less complex bezel locking mechanisms -- as first introduced on the Omega Ploprof in 1970 and in its contemporary variant in 2009 -- can also be found at the Hublot Subaquaneus, the Squale Tiger, a few versions from UTS, Germano, and Glycine, and, of course, in elderly Yema models.

Citizen Promaster 1000, before (above) and after (below) placing the bezel and submerging
2. Internal bezel
Most likely introduced by Aquastar from the 1960s. In this structure, the bezel is located within the watch and can be thus protected by the crystal, giving the watch a more elegant appearance. The bezel can only be worked using a (usually additional) crown, quite often in both directions (exceptions include the Audemars Piguet Royal Oak Offshore Diver, Hublot Oceanographic, etc.). Disadvantage: An extra opening in the case (except possibly for the first Aquastar models, and the recent Maurice Lacroix Pontos S, in which the chronograph pusher also functions the bezel) and often a rather small crown to fumble with. The more secure it is designed (unidirectional, screw-in), the less practical it becomes for diving.

In 2002, Eterna introduced, with its KonTiki Diver, an intriguing first blend of both theories: the internal bezel could be controlled from the outside, a concept that initially permitted a water resistance of 200 meters and, in 2005, around 1,000 meters together with the more radical-looking Concept Diver.

In 2014, IWC went all the way and appears now to be supplying, for the first time, the best of both worlds: The present IWC Aquatimer family comes with a system, called Safedive, that unites a unidirectional internal bezel that can only be rotated with a ratcheting external bezel (that could be transferred in both directions, but only counter-clockwise for adjusting the inner bezel). The IWC video below demonstrates how it works: Want to know more information click Citizen Ambiluna