The most famous chronograph watch in the world is debatable, but there is no debate. It’s the Omega Speedmaster Professional:

Omega Speedmaster Chronograph Men’s Manual Wind Watch Stainless Steel Brown Dial 311.30.42.30.13.001
The Rolex Daytona fans can moan all they want, but when it comes to mechanical chronographs, how can you beat the Omega Speedmaster Professional?
This watch, after all, was the
first and for the longest time, ONLY watch worn on the moon. Its most touted use, however, was when it was very prominently used to time the afterburner rockets that allowed the crippled Apollo 13 spaceship to fly home.
There are no doubts that this is one of the most historically significant watches out there, and if you ever looked its bezel, that is, the rim of the watch, you will probably notice that it’s got a Tachymeter (or Tachymetre, or Tachometer):

Now what exactly IS a tachymeter you might be asking?
Well a real tachymeter is certinaly more complicated than a plastic rim with some numbers on it, but when it comes to watches, a tachymeter is used to measure speed, but there are some caveats…
Here’s how it works. It takes pretty much any unit of distance, such as a mile, a kilometer, etc. and it tells you how many of it your are doing of it in an hour. You start the chronograph and use it to measure the elapsed time it takes you to travel a certain measure of distance such as a mile, nautical mile, and what have you.
Okay, here we go:

For all intents and purposes, please do not focus on anything else on the watch EXCEPT the hand that it is pointed directly at the 12 o’ clock position. I know a lot of people are thinking this is probably the seconds hand, but it is not. In most mechanical chronographs this is the hand that times stuff. (See the sub-dial at the 9 o’clock position with the numbers ‘20,’ ‘40,’ and ‘60,’ on it? That is what is measuring the seconds. If the chronograph is not engaged, the hand pointing at the 12 o’clock position will not move).
Okay let’s say we are traveling in a very fast rocket powered car with no speedometer. We want to know how fast we are going but don’t have the faintest of idea, but we do have an odometer so when a new mile starts we engage the chronograph…

After the odometer travels that one mile we stop the chronograph, and as you can now see, the chronograph hand says it took us about 37 seconds to travel that mile. If you look at the tachymeter reading, you can see that you have been traveling at about 97 miles per hour. That’s pretty fast!
I’m sure you can see where some problems with this lie…
First of all, you would have to know how long a certain unit of distance is. You would have to know how long a mile is, you would have to know how long a kilometer is, etc…
Secondly, and most important, you would have to be going at least 60 of that rate of speed for the tachymeter to be of any use. If you take longer than a minute to travel that unit of distance you are done for.
It is so stupid, but it sets a perfectly reasonable speed to be the bare minimum of its use. Whoever regularly goes up to 300 miles/hm per hour is a person I’d like to meet, and if he uses his watch as his only means of determining that speed, that’s pretty cool.
To a lesser extent a tachymeter can also be used to measure the total distance you have traveled, but that would requiring you to be traveling at a constant speed. Bottom line is that I know why they have it the Omega Speedmaster Professional, it’s tradition, but why is it on so many automatic chronographs in this modern age still baffles me.
It is not needed, no one uses it, most people are not “speed masters,” so why can’t we just get rid of it?
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