How To: Read & use the markings on your bezel.

[gioarmani]

(Admin: feel free to sticky or pin this, if applicable. Thanks!)

As simple as this topic sounds, a good number of newcomers to the horological world might not understand the true functions of the bezel on their very own wrists. So, here's a quick & easy summation on what those numbers mean.

There are a few different types of bezels marked for any number of things, such as calculation of distance, time, speed, etc. But the two most popular marked bezels are for calculating speed (e.g. the Rolex Daytona, the Omega Speedmaster, the Panerai 212):

And bezels for counting down time (e.g. the Rolex Submariner, the Omega Seamaster, the IWC Aquatimer):

The bezel on a chronometer such as the Daytona, is essentially a speedometer, like the one on your car; it's used to clock speed, but on a distance of one mile, only. So the numbers on the bezel actually represent MPH (miles per hour). In order to be able to use the bezel as such, the watch must come with a stop-watch function, or a chronograph.

>>>>>Here's how you use the bezel in conjunction with the chronograph, to clock the speed of a moving object:

If the distance between point A & point B on a track (be it for horses or cars) is exactly 1 mile, then the second the moving object you're timing passes point A, you start the chronograph--the second the moving object passes point B, you stop the chronograph. Wherever the large second hand on the chronograph stops (on the bezel), is the exact MPH the object was traveling. In the picture below, a car clocked on the track between points A & B, appears to be traveling 160 MPH:

However, an exact reading only applies to an object moving at an exact speed (i.e. only going 160 MPH, no less, no more). If a car is varying in speed (i.e. it's doing 150 MPH in the turns and 170 MPH on the straight-a-way, the bezel is telling it's average speed; 160 MPH.

An easier example would be, if you're driving at 60 MPH, then you're traveling exactly 1 mile for every minute that passes. Which is why the 60 is at the top of the bezel, at the 12 o'clock position--if it took a full 60 second rotation of the chronograph hand for you to travel between points A & B--the time to travel exactly one mile--then you're going exactly 60 miles per hour. And that's how this particular bezel is used as a tachymeter, or speedometer.

This is why, as you follow the hands clockwise on a Daytona, the bezel markings go down in number; the longer it takes you to travel a distance, the slower you're traveling it.

Of course, using the bezel as a tachymeter only applies to an object traveling at a constant rate of speed. For instance, if a car was going from 0 to 60 MPH, and this took 8 seconds, if you're matching the chronograph hand to the bezel, you'll see 8 seconds reflects a speed of 400 miles an hour--this is obviously incorrect:

By doing this, you're calculating time and not speed (i.e. 0-60 MPH = 8 seconds, not 0-60 MPH = 400 MPH), so you should be matching the chronograph hand with the seconds markers on the dial and not the markings on the bezel.

>>>>>Here's how to use the bezel on a diver's watch as a countdown clock:

Unlike a tachymeter bezel (or tachometer, for we Americans )--which starts at 400 MPH and counts down to stop at 60 MPH at the 12 o'clock position--a diver's watch bezel is labeled 0-60 minutes (and line up exactly with the hour markers on the dial), and are labeled counting up, traveling clockwise with the watch hands, as such:

A watch without this bezel cannot be called a true "divers watch" (as it does not not comply with ISO 6425 & DIN 8306 standards for divers safety).

The first step is to align the bezel pearl (the 0 hour marker on the bezel) with the minute hand on the watch; this must be done immediately upon starting your dive (the bezel is unidirectional--it only rotates counter-clockwise, so you don't bump it when diving and accidentally move it back to a wrong position, giving you a false reading as to how much air you have left).

If you're starting your dive at 10:45, align the pearl with the minute hand at the 45 minute mark:

Now, in order to use it properly, you'll be coordinating the watch's minute hand in conjunction with the bezel, and not the dial. So, if you're scuba diving and know your tanks only hold 45 minutes of air, then it's time to emerge when the minute hand reaches the 45 minute mark on the bezel. 45 minutes from the start of your dive at 10:45, would be 11:30:

Of course, these types of diver's watches are only intended for scuba-diving, and not deep-sea or saturation diving, as most scuba dive watches such as these, can't go to those levels without an HEV (Helium Escape Valve).

Deep-sea divers must first have their bodies decompressed in a diving bell before descending to such incredible depths, and are breathing a mixture of gasses containing lowered nitrogen & oxygen, and more helium & hydrogen (because oxygen becomes toxic at high pressures, causing seizures and other problems, and nitrogen becomes poisonous in the bloodstream).

The primary reason saturation divers don't need the bezel is because they're breathing a completely different mixture of air, fed to them via tubes, and not compressed air tanks, which would implode at those depths; they dive "at saturation", meaning that because they stay for extended periods at such depths, their body tissues become saturated with nitrogen. In fact, they really have no time limit to their dive, other than that caused by the cold and local conditions. They then do their decompression inside decompression chambers, once they reach the surface. So, a timing bezel is not an absolute requirement for saturation divers. In fact, professional divers might not even be able to manipulate a timing bezel with their thick gloves.

And this is why divers watches look & function as they do, in coordination with the bezel.

Of course, sometimes you discover both on the same piece; for deep-sea dive purposes only, occasionally a watch with an HEV will combine both the chronometer/stop-watch and the diver's bezel, on models such as the Omega Seamaster Professional chronograph:

Hoped this little explanation helped, and thanks for your time.

[jeroen1985]

Thnx dude very very usefull topic!!! Now I understand the bezel fucntion of the UPO!!

[dluddy]

Great contribution Gio. Thanks for sharing

And for your Jessica Alba animated signature

[gioarmani]

You're more than welcome!

[scoobs1971]

Good topic Gio!

Here's another scale: The Telemeter

Chronographs also refer to a number of other measuring devices that were only developed for watches in recent years. One of these is a telemeter, which is a series of numbers on the bezel that are set according to the speed of sound. By using the stopwatch to measure the number of seconds that pass, for instance, between a flash of lightning and the sound of thunder, the telemeter numbers will indicate how many meters away the sound source is. This tool was especially useful in the military, where it could be used to estimate the distance of enemy artillery by calculating the time between a flash of light and the sound of the shot.

[Pugwash]

Surely if diver's watches bezels were for timing remaining air, they'd be in reverse.

[hyster]

Very much enjoyed reading that, Gioarmani.

Well done.

[Pugwash]

A watch without this bezel cannot be called a true "divers watch" (as it does not not comply with ISO 6425 & DIN 8306 standards for divers safety).

Entertainingly, this does in fact mean your average Panerai Diver's watch cannot be called a Diver's watch.

[DemonSlayer]

Very informative read. I didn't quite understand what the bezel or the chronographs used for, now I do Thanks gioarmani!

[gioarmani]

Good topic Gio!

Here's another scale: The Telemeter

Chronographs also refer to a number of other measuring devices that were only developed for watches in recent years. One of these is a telemeter, which is a series of numbers on the bezel that are set according to the speed of sound. By using the stopwatch to measure the number of seconds that pass, for instance, between a flash of lightning and the sound of thunder, the telemeter numbers will indicate how many meters away the sound source is. This tool was especially useful in the military, where it could be used to estimate the distance of enemy artillery by calculating the time between a flash of light and the sound of the shot.

Now that's interesting--I've never seen that before.

Entertainingly, this does in fact mean your average Panerai Diver's watch cannot be called a Diver's watch.

Possibly. But almost all of this is taken from gen manuals.

[Pugwash]

Possibly. But almost all of this is taken from gen manuals.

You'd be surprised how wrong some gen manuals are, especially on the subject of He valves.

[FxrAndy]

Bear in mind that the tachymtre is not just for miles per hours per hour but for units per hour, if you travel 1 kiliometre in 60 seconds you are traveling 60km per hour. also if you fill 1 liter of water from a tap in 60 seconds then your tap will give out, 60 liters per hour, or as mine at home 1 liter in 10 seconds then that is 350 liters per hour.

[scoobs1971]

Navitimer owners may wanna check this link hxxp://home.xnet.com/~cmaddox/breitling/Instructions/navitimer/navitimer_instructions.html

[randomfunk]

Useful topic, cheers!

[Johnkaz]

We never stop learning useful facts on this forum. Thank you my Tag has that tachymetre thing, now where are my car keys.

Thank You.

Johnkaz.

[gioarmani]

Lol.

[Victoria]

How many times do I have to read a Gioarmani post, and think, "Dang, this guy only posts useful stuff". So many times!

Thank you so much. I love learning from your accomplished reviews.

[spa]

I am not a diver myself but having a close friend who is a diver and, he's got his "instructor" diploma from PADI, i can assure you that diving bezels of diver watches (like Rolex Omega etc.) are of no use for a serious diver who cares about his underwater safety.

The reason is that remaining air/diving time is not static when the diver dives, and depends of the depth changes and other factors too...

That's why both pro and amateur divers rely entirely on diving computers to have a constant and accurate information about the remaining air and time.

Even specialized diver watches like Citizen Promasters, cannot give accurate enough readings as a diving computer can.

But one thing's for sure...A Diver's Rolex Submariner/Sea-Dweller or Omega Seamaster is only just a "gadget" that matches his/her "I am a diver" profile and nothing more.

Don't rely on them for diving. I am sure you don't...

[spa]

I will agree with you about the calculating thing that the dive bezel is supposed for, with one exception:

that works only if the diver stays at a certain depth and does not go deeper or higher than that level.

That hardly applies in real life diving i think. At least that's what i was told about...

[Pugwash]

That's why both pro and amateur divers rely entirely on diving computers to have a constant and accurate information about the remaining air and time.

Back in the day, a bezel was a diving computer.

[southcoast68]

Omega Speedmaster chronographs were also available with a "pulsations per hour" bezel, which I can only assume was intended for medical purposes (measuring heart rate). Maybe someone here can verify this for us.

[ratchpot]

As I already mentioned over on RWI, the text about the bezel on a dive watch being used to calculate remaining air time is wrong and should be changed. The only thing a dive bezel is useful for when diving is to track the duration of the dive (or another specific event that requires timing, such as a safety stop).

That's why both pro and amateur divers rely entirely on diving computers to have a constant and accurate information about the remaining air and time.

That's not true as regards remaining air. The majority of pro and amateur divers still rely on submersible pressure guages to relay information about remaining air.

[yt74]

Very useful!

[abat]

As Andy pointed out the Tachymeter function can also be used to track KPH if you use a Kilometre as the unit of measurement. Some watches (like the Chromomat Evolution) have both on the scale so you can convert between the two, so at the 12 o'clock position it has 100 and 60 (although by my reckoning that is not quite accurate).

[Ham 'n' Pickle]

I would go along with all the previous comments about this being very useful info.

The only thing I would like to see more of on watch bezels is a countDOWN bezel not a countUP one. My ideal watch would be a Breitling B-1 which has the numbers on the bezel starting at 55 on the number 1 baton a reducing to 5 on the number 11 baton.

This makes more sense to me to set the bezel number on the minute hand and count down to an event happening in that number of minutes, (set the bezel number 25 at the minute hand and in 25 minutes the minute hand will be at the zero mark whilst giving you a running value of how many minutes left until the event)..

Ham 'n' Pickle.