What is tachymeter?

A tachymeter is a scale found in chronograph watches and is used to measure speed and distance. It is found just inside the dial from the bezel or might be inscribed in the bezel itself in some watches. You could use a tachymeter scale on a standard time-only watch as well, but for proper use and calculations, they need the ability to start and stop timing, which is the reason why you see them mostly on chronographs only.

 This scale starts at a 7-second mark at 500 units of speed. Some models also start their scales at 6 seconds and 600 units, or 9 seconds and 400 units. The basic mathematical equation T=3600/t is used to calculate the speed, where T is the tachymeter scale value and t is the elapsed time. This equation is used to convert elapsed time into speed.

What is tachymeter in the watch?

Mechanical watches like watches with a tachymeter scale have helped measure distance, time, speed for a long time. They date back as far as the chronographs. By the 1930s, an ample of brands had started to produce wristwatches with tachymeter scales. In the 1950s, the chronograph became a must-have sports watch. Surprisingly, a tachymeter holds the power to make your chronograph feel more useful, to this very day. 

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How to use tachymeter?

The use of a tachymeter basically depends on the relationship between speed, time, and since, something that all of us have read in our elementary school. Let us tell you how exactly you can benefit from this wonderful feature in your watches.

  • How is speed measured using a tachymeter?

The first thing you need to calculate speed is the distance between two points, and in a tachymeter, the points are designed for a single unit, either a mile or a kilometer. 

You will be needed to follow these given steps to calculate the speed:

  1. Find the distance between two points.
  2. Start the chronograph as soon as the object passes through Point 1 or the initial point.
  3. Stop the chronograph when the object crosses Point 2 or the final point.
  4. Observe the point at which the chronograph seconds hand falls on the minute track.
  5. Line up the hand with the tachymeter scale, and you’ll get your required speed.

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  • What to do when the distance is shorter than a mile?

Since the chronograph measures the distance in a single unit, you will have to base your measurements likewise. Let’s say you have to find the speed of a person running in a race, the distance of which is ¼ of a mile, you will have to look at ¼ of the tachymeter measurement. 

Tachymeter

The same technique can be used to measure the time when it is more than 60 seconds. You can also find the amount of time you take to produce something in an hour, following this method. Let’s say you take 45 seconds to fill the air in a balloon and tie it up. When you look across the tachymeter scale, it lines up with 80, which means you can fill the air in 80 balloons at an average, in a given time period of 1 hour.

  • How is the distance measured using a tachymeter?

Measuring distance and speed is quite similar. When you were measuring the speed, you needed to know the distance between two points. Now, if you’re measuring distance, you will be required to know your travelling speed, and you must also make sure that this speed is constant.

You can find the distance by following the given simple set of instructions:

  1. Find out your constant travelling speed.
  2. When you cross a certain point, start your chronograph.
  3. When you have travelled the speed lining up with the tachymeter scale, stop the chronograph. 
  4. When the second’s hand of the tachymeter scale is at your travelling speed, it means you have travelled a distance of one mile.

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Hence, tachymeters can be used to measure both, time and distance. In the initial use of this method, you might feel a little uncomfortable, maybe due to the math. But, we assure you, this is a great feature on your watch, that will certainly earn your affection in a few days if you keep practising it.

How to Choose Chronograph and Tachymeter Watches
Image from watchesly.com

What are the drawbacks of a tachymeter?

Most tachymeters start at a 5 or 7-second mark. If your event falls between 0 and 5 seconds, there are absolutely no marks on the tachymeter scale to line up with the speed. 

Also, most chronographs have a sweeping second hand which keeps gliding between each mark. However, some watches also have a deadbeat seconds hand which jumps from mark to mark. This feature mostly creates difficulty in measuring decimals of seconds. These deadbeat hands-only read the whole numbers in the scale. This is one feature that you can take into consideration when you’re buying a chronograph. 

What is the accuracy of these measurements?

The accuracy of your measurements will primarily depend upon the sharpness of your timing. Starting or stopping the chronograph just a second early or late will have an impact on your speed/distance calculations. But, realistically speaking, it is quite possible to be reasonably accurate in your calculations. The slower you’ll be going, the more accurate your measurement should be.

We hope this helped you understand how exactly can chronograph and the tachymeter scale in your watches help you measure speed as well as distance. However, the main intention of a tachymeter scale is to measure speed. The most important thing you need to keep in mind is that the units of your speed and distance must match. If you measure your time over a mile, you get your speed in mph. the same holds for a kilometer as well.

Well, we guess it’s finally time to put some of those math lessons to use (yay, finally!). We hope this helped you in learning all about tachymeter scales, how to use them to measure speed and distance as well as some of its limitations, factors that you must know if you’re planning on buying one.