Dive watches, chronograph watches, GMT’s… Modern horology has a range of watches competing for buyers attention. Many sports or “professional” watches offer timepieces with a numbered ring which has different uses depending on which application the watch has been designed to assist with.
Dive And Seafaring Watches
The dive watch is defined by its bezel which is used to count the length of time spent underwater and therefore the amount of time before divers need to head to the surface. It is not an indicator of how much air is left in the tank. The method of setting and using the bezel is simple. Before descent, the triangular bezel marker (which is usually set at 12 when not in use) is aligned with the minute hand on the watch. This allows the elapsed time to be viewed quickly and at a glance. The triangular marker contains a lume pip at its centre so that it’s visible in murky and low light conditions. Dive bezels are unidirectional for safety purposes. If the bezel is accidentally knocked underwater it will only move in one direction – anticlockwise. This gives you more time to ascend to the surface rather than less.
The bezel on this Submariner has been set as an example. At 3.52, 30 minutes will have elapsed.
Not all dive watches have external bezels. Some use an internal bezel system which, although a little more “fiddly” to set reduces the risk of movement while underwater. The Audemars Piguet Royal Oak Offshore Diver being one example. The internal bezel is moved by unscrewing and rotating the crown at 10 before re-screwing to ensure ensure water resistance.
While diving is the “official” application for these watches, their real world use is much more varied. Eggs – 3 minutes from the point of boiling. Pizza – 12 minutes. Spaghetti – 9 minutes. Lasagne – 45 minutes and car parking anything up to an hour.
Chronograph watches and Tachymetre bezels.
Tachymeter bezels are usually found on watches with chronograph functions. The tachymetre bezel is used for measuring either speed, or distance. The most notable chrono/tachy combination watches are the Rolex Daytona available here – https://www.officialwatches.com/our-watches/#q=daytona&hPP=16&idx=products&p=0 and Omega Speedmaster available here – https://www.officialwatches.com/our-watches/#q=speedmaster&hPP=16&idx=products&p=0.
One for motorsport and one for space but they both perform the same functions.
Chronograph watches utilise a different feature to standard 3 hand watches, one which can often confuse new purchasers. The seconds hand/counter of the watch is housed within one of the sub-dials on the watch face. The large slim hand resting at 12 is the hand which revolves around the dial as part of the chronograph feature. It isn’t a traditional seconds hand. If it isn’t moving, this doesn’t mean that the watch has stopped, it just means that the chronograph isn’t engaged. Timekeeping seconds should be ticking away quite happily in a sub dial. It is wise to note that running the chronograph hand as a permanent centre seconds hand can sometimes slow a watch down as additional energy is being diverted to the chronograph hand which can drain “wrist or wind power” from the timekeeping of the movement, so I wouldn’t advise constant running if you value +0/-0 accuracy.
The chronograph element of these watches is simply explained – it’s a stopwatch. Press the 2pm button to start, press again to stop, and press the 4pm button to reset the chronograph hand to its 12 position. When you use the chronograph feature in conjunction to the tachymeter scale around the bezel though, things start to get interesting. If you don’t get out much. 😉
Mathematically, the equation to calculate is T=3600/t. The “T” is the tachymeter scale value, “t” is the elapsed time and 3600 is the number of seconds in an hour. Fortunately, we can afford to forget the algebra as the bezel will do the work.
Tachymetres can be used to measure miles or kilometres, so long as you decide which unit you’d prefer to use before beginning. For the purpose of demonstration we will stick to MPH.
To measure distance successfully, you first need to have an accurate visual representation of the distance that you are going to use to make your measurement. For example, the distance between mile markers on a race track.
Knowing that the distance between the two points = 1 mile, you would be able to measure the speed of a car by starting the chronograph when it passes marker 1 (blue X), stopping when it reaches marker 2 (red X), and checking the readout on the bezel tachymeter scale (67 MPH)
You can also use the bezel to calculate distance, but you would need to keep your speed constant.
Using the Daytona above, let’s say you’re travelling at 67mph. Start the chronograph when speed is constant, stop when it hits the 67 marker on the bezel. When you hit stop – you will have travelled 1 mile, and it will have taken you 54 seconds.
GMT and 24 hour bezels are, to the relief of some (me), much easier to use.
In this image the GMT hand (blue) is set to display the same time as local time. It is reading 10am along with the rest of the watch. The GMT bezel is reading the standard 24 hour scale so when the GMT’s hand hits 22, it will be 10pm.
The GMT hand can be moved to line up with the 6 on the bezel if you wanted to track time in New York, which is 4 hours behind our local time, so the watch would read 10am local time, with blue gmt at 6 on the bezel = 6am NY.
The bezel on this GMT has been used to calculate a third time zone by moving the bezel rather than the GMT hand. If the bezel was set to triangle at 12 then it would read at 16 on the bezel – 4pm, same as the hands.
We can see that the bezel has been moved so that it reads 21.00 (9pm) at the 12.00 point of the watch. It has been moved 3 hours back, to match the time in Buenos Aires which is 3 hours behind local time here (GMT). To read the watch in full – local time is 4.11 pm with the GMT hand pointing to 13.11 – 3 hours behind GMT.
24 Hour Explorer Bezel
The 24 hour bezel was originally developed to indicate the difference between day and night for spelunkers (cave explorers) but its use has modernised somewhat. Spelunkers used to set the time to 10am and the orange hand to 10 on the 24 hour scale indicating morning. If they later read the watch inside the cave and it was reading 8.00, they could check the position of the orange hand against the bezel to see if it was am (8) or pm (20) using the 24 hour scale to distinguish night and day. This saved them from not knowing if it was day or night and becoming disorientated. Note that it is the orange hand that tracks 24 hour time or different time zones, not the hour and minute hand of the watch.
This Explorer II is using the 24 hour bezel and orange hand to track a different time zone rather than day/night. The local time is reading 1.53 and the orange hand is indicating close to 16, so the time on the bezel is 3 hours ahead of local time at almost 4pm. Easy to read once you get the hang of it.
Hopefully this quick guide has given you some insight into getting the most out of your watch.