Details behind the Bezel of the GMT and Diver's Watch

For those who have only recently discovered their newly found passion for horology, you may not know what a bezel actually is. Each watch has a bezel, and is simply put, the outer ring that surrounds the face of the watch. It’s main purpose is to protect the crystal glass and inner workings from the inevitable daily wear and tear of life. This was all there was to a bezel up until the 1950’s, when watchmakers discovered a way to add more function to a watch without complicating the movement, resulting in an external watch bezel with various different functionalities. The uses of a bezel in modern times go beyond the protection of the crystal and extend to monitoring speed, calculating distance or even measuring your heart rate. We’ll stick to some traditional forms for now and focus on two very special types: the GMT & Diver's bezel.

The history behind the GMT

The GMT (Greenwich Mean Time) watch has a bit of an interesting history with partial origins arising from ancient Egypt, as it was the Egyptians who divided the day into 24 hour increments through the observation of the sun and stars. The remaining majority of its origins are all thanks to aviation thousands of years after. It was in 1952, when the first intercontinental flight from England to South Africa changed the entire game. Commercial air travel has allowed us to switch time zones in a short amount of time - what took weeks and months before now took several hours. At the time, pilots required the GMT time for efficient navigation and communication as well as the local time of the time zone that they were in. It was this necessity that drove Pan Am to approach Rolex to accommodate their needs and build a watch that has the capability to track two separate time zones. In 1954, the legendary Rolex GMT-Master was born.

The additional watch hand

Most watches have an hour and minute hand, a GMT watch has a third hand also simply known as the “GMT Hand”. Whilst a standard watch keeps 12 hour time, ie. the hour hand will around twice a day, the GMT hand goes around the dial once per day which makes it a 24 hour dial. These are usually shaped as an arrow and have a different colour than the hour and minute hands.

Rotating bezel

You may be wondering, how does a watch have a 24 hour display if the watch face only has 12 hour increments? This is exactly where the bezel comes into play. GMT’s have a rotating bezel with 24 incremental markings around its exterior which mark the 24 hours in a day. When the marker on the bezel is straight straight to 12 o’clock, then the GMT hand is also going to tell the same time as the minute and hour hands. (As pictured below) In order to set the time for a different time zone, all you do is rotate the bezel. Depending on which time zone you want, you can rotate it backwards or forwards. For example, you rorate it 4 hours forward if you want to sync it with a place that is 4 hours ahead. The minute and hour hands tell you your local time, and the GMT hand will show the other time zone.

The Diver’s Bezel

The bezel on a diver’s watch is so distinctive, it’s hard not to notice it. It’s roots go back to the 1950’s, when Rolex and Blancpain introduced a watch to track the time a diver spent at the bottom of the ocean or underwater – a useful feature to prevent divers from exceeding their time limit. The bezel is either divided into 60 minutes or 12 hours and has a luminescent zero marker which is often in the shape of a small circle or triangle.

How does it work?

When a diver is about to embark on their descent, the 12 o’clock marker on the bezel is aligned with the minute hand, this allows the elapsed time - which is up to 60 minutes - to be clearly seen on the bezel. The unidirectional function works counter-clockwise and ensures that in case the bezel is moved accidentally, the time that has already gone by underwater would be shown as longer than the actual time to allow the diver to swim back up safely. The divers usually has to track the remaining time themselves, therefore if your watch shows that you’ve been under the water for 35 minutes, then you need to subtract this number from 60 to see how much is remaining, which in this case would be 25 minutes. The bezel can be turned so that the 25 mark on the scale is against the minute hand, which ensures that it will take 25 minutes for the minute hand to reach the zero marker.

External vs Internal

When it comes to the construction, there are two types of bezels. The external bezel was the first to be introduced and is still the more popular one. As the name indicates, an external bezel is on the outside of the watch whereas an internal bezel is constructed under the watch glass and runs with an additional crown. Although the internal bezel protects the diver from accidentally moving the marker, it can be harder to control it than an external one without a proper grip. The external remains to be user friendly however is prone to debris or salt getting between the case and bezel, it also poses the risk of the bezel being moved accidentally or being damaged. Several brands have come out with models that fuse both together. The one that really caused an excitement in the watch industry was when IWC relaunched the Aquatimer with the Safedive feature. This fused a unidirectional internal bezel that can only be rotated by ratcheting an external bezel. The external bezel could be moved in both directions, but only counter-clockwise when adjusting the internal bezel preventing the accidental change of dive time.

One doesn’t have to be a professional diver or a pilot to enjoy these magnificent timepieces. Whether for sport, travelling or just simply wearing an intricate piece of art on your wrist on a day to day basis, you’ll be sure to find a use.  We have quite the selection to offer to you here at CHRONEXT, why not browse through the collection and start planning your next adventure.