Automatic Watches
How to Read a Tachymeter Bezel (And When You’ll Actually Use It)
By Argos Watches
Sports watches have become more sophisticated and useful over the years. Among their common features, the circular scale on the edge, called a tachymeter, stands out. It's used to measure speed based on how much time passes, and it remains a popular design element even today.
In this blog, we'll show you step by step how to understand a tachymeter and offer some helpful tips along the way.
In this blog, we'll show you step by step how to understand a tachymeter and offer some helpful tips along the way.
What is a Tachymeter Bezel?
A tachymeter scale is a set of markings, usually in a circle on the edge of a watch face, that allows you to figure out how fast something is moving. The word "tachymeter" comes from old Greek words meaning "swift" and "measure."
While the first stopwatch was created in 1821, these features weren't added to wristwatches until 1913. Since a stopwatch is needed for a tachymeter to work, the tachymeter quickly followed onto wristwatches.
Wristwatches with a tachymeter became very popular as car racing grew and air travel increased. Your tachymeter works with the stopwatch part of your watch to measure the time it takes you to cover a set distance. You might notice the edge has many numbers and marks, which can look confusing at first. But don't worry, getting the reading is straightforward and makes sense once you understand it.
While the first stopwatch was created in 1821, these features weren't added to wristwatches until 1913. Since a stopwatch is needed for a tachymeter to work, the tachymeter quickly followed onto wristwatches.
Wristwatches with a tachymeter became very popular as car racing grew and air travel increased. Your tachymeter works with the stopwatch part of your watch to measure the time it takes you to cover a set distance. You might notice the edge has many numbers and marks, which can look confusing at first. But don't worry, getting the reading is straightforward and makes sense once you understand it.
How to Use a Tachymeter
A tachymeter bezel is a circular scale on the watch that can be used to measure speed or distance.
Measuring Speed: A tachymeter is a great tool for measuring speed. To do this, you'll need to know a fixed distance, like one mile or one kilometer.- Start your watch's stopwatch using its button as you begin your journey.
- When you know you have traveled exactly one mile or one kilometer, push the stopwatch button again to stop it.
- Look at where the second hand has stopped on the tachymeter scale. The number it points to shows the speed of the car or whatever vehicle you're using.
This works because of a simple calculation. There are 3600 seconds in an hour. If it takes your vehicle 60 seconds to finish that mile, then 3600 divided by 60 equals 60. So, you're traveling at 60 miles per hour. In this case, your second hand would point to the 60 mark on the tachymeter (which typically corresponds to 60 seconds).
The nice thing is that because this is based on a mathematical idea, you control the type of distance you're measuring. Even if you don't use a full mile, you can still get the final calculation with a little extra math.
Keep in mind that many tachymeters don't give a direct reading for times beyond 60 seconds. The simple reading straight off the tachymeter scale will only work if you're going at higher speeds. Tracking slower speeds will need a bit more calculation.
The nice thing is that because this is based on a mathematical idea, you control the type of distance you're measuring. Even if you don't use a full mile, you can still get the final calculation with a little extra math.
Keep in mind that many tachymeters don't give a direct reading for times beyond 60 seconds. The simple reading straight off the tachymeter scale will only work if you're going at higher speeds. Tracking slower speeds will need a bit more calculation.
Calculating Slower Speeds
For someone moving at slower speeds, like a runner, the calculations take a little more thought. This is where the flexibility of using any distance comes in handy.
- Pick a distance to track while running, for example, 500 feet. Using the same method as above, you'll start your stopwatch with the button as you begin running.
- Once you cross the 500-foot mark, stop the stopwatch. Note the time in seconds. Let's say it took you 30 seconds to run 500 feet. Your tachymeter is going to show you a very high speed, like 120 miles per hour, which is obviously not correct for a runner.
- To calculate your actual speed, you need to remember that 500 feet is a little more than a tenth of a mile (it's exactly 10.56 parts of a mile). So, you must divide the number on the tachymeter (120) by 10.56. That gives you roughly 11.4 miles per hour, which is a much more realistic running speed.
Calculating Higher Speeds
Tachymeters are also popular for vehicles that travel much faster, like aircraft. If your watch doesn't measure beyond 60 seconds directly, you'll have to do some more math here too.
In this case, you'll need to adjust your fixed distance measurement. It's easy enough to change your standard "1 mile" to "10 miles." Let's say your watch shows it takes 20 seconds to travel your new fixed distance of 10 miles. The tachymeter might give you a reading of 180 miles per hour. But since you were measuring over 10 miles, you'll multiply this by 10. This gives you an actual speed of 1800 miles per hour.
In this case, you'll need to adjust your fixed distance measurement. It's easy enough to change your standard "1 mile" to "10 miles." Let's say your watch shows it takes 20 seconds to travel your new fixed distance of 10 miles. The tachymeter might give you a reading of 180 miles per hour. But since you were measuring over 10 miles, you'll multiply this by 10. This gives you an actual speed of 1800 miles per hour.
Measuring Distance
Even though the tachymeter wasn't specifically made to measure distance, you can use it that way. This method relies on you traveling at a steady speed. It's a way to measure average distance, so to get a somewhat accurate result, you must maintain a consistent speed. Follow these steps to measure distance using a tachymeter bezel:
- Decide on a fixed speed you can keep throughout the test.
- Begin at your starting point and start the stopwatch when you begin moving.
- Stop the stopwatch once you reach the number on the tachymeter scale that matches the speed you tried to maintain during the test.
- The stopwatch's second hand will then point to the distance you have traveled on the tachymeter scale.
Understanding the Tachymeter and Stopwatch
A tachymeter scale is that complex-looking circle of numbers (usually from 700 down to 60) that runs along the edge of your watch face, specifically on watches with a stopwatch function. Despite its busy look, the tachymeter serves a very helpful purpose: it changes time measured in seconds into a speed measured in "units per hour." So, a tachymeter can tell you how fast a car, a plane, or even a runner is moving over a set distance.
What's special about a tachymeter is that it works independently of a specific unit of distance (like miles or kilometers), as long as you use the same unit throughout your calculations. So, a reading of 120 on the tachymeter scale can mean 120 miles per hour or 120 kilometers per hour, depending on what unit you're measuring.
What's special about a tachymeter is that it works independently of a specific unit of distance (like miles or kilometers), as long as you use the same unit throughout your calculations. So, a reading of 120 on the tachymeter scale can mean 120 miles per hour or 120 kilometers per hour, depending on what unit you're measuring.
When You’ll Actually Use It
While a tachymeter can seem like a very specific tool, its main job is about quick calculation. Beyond timing a race car or a plane, it can be useful in everyday situations where you need to measure how many units of something happen over a known amount of time or distance. Think about:
Production: Timing how many items are made per hour on a factory line.
Sporting Events: Figuring out the speed of a cyclist over a specific part of a course.
Travel: Estimating your average speed between two points on a road trip, if you know the distance between them.
The key is always having a fixed distance and measuring the time it takes to cover it. While the specific calculations might change depending on whether you're dealing with very fast or very slow movements, the basic idea of the tachymeter stays the same. It's a clever mathematical shortcut right on your wrist.
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