A tachymeter is a scale, typically along a watch’s bezel or surrounding the dial. The function allows the user to measure the rate of any consistently occurring event over a measured period. This could mean your driving speed over a set distance or how many watch straps a factory produces per hour.
A tachymeter is always accompanied by a chronograph, which measures the elapsed time used for calculating the rate the tachymeter measures.
Many consider this feature outdated due to modern technological advancements, such as the smartphone in your pocket, but you can still find a tachymeter on many modern chronographs.
It may be because it is a fantastic triumph of engineering. Perhaps it is the rich history behind its creation and uses over the past decades in motorsports and aircrafts, or maybe it’s just because it is an aesthetically pleasing and helpful feature to have on your watch.
Suppose you are looking for a watch that will root you to a significant period of watchmaking when wristwatches were more than just jewelry. In that case, a chronograph with a tachymeter is an excellent choice to add to your collection. Let’s take a closer look at this exciting complication.
What is a Tachymeter?
This tool is a watch complication used to calculate the rate of an event over a recorded amount of time. The tachymeter is a scale of numbers on the watch’s bezel or surrounding the watch’s dial.
Tachymeters are particularly useful as they can be used in various industries and situations, from racing to measuring production speed in a factory.
Types of Tachymeters
Three main types of tachymeters can be found on the market.
The first and most common type is the fixed bezel tachymeter which describes a tachymeter where the scales are in fixed positions surrounding the bezel. When you think of a tachymeter, this is most likely the one that pops into your head, used in many of the most famous chronographs, such as the Rolex Daytona and Omega Speedmaster.
A snail-type tachymeter can be used to measure slower velocities. It typically has three colored rings etched in the middle of the chronograph’s dial.
The last and final tachymeter type is a rotating bezel tachymeter. This specific type is unique because it does not need to be reset for every base unit, I.E. every kilometer. By rotating the bezel, every kilometer’s average speed can be measured independently. These chronographs are more expensive as fitting a tachymeter onto a rotating bezel is complex and adds complication.
In this article, we will primarily refer to the fixed bezel tachymeter, as this is the most common type used in watches.
How to Read a Tachymeter
Fixed bezel tachymeters work very simply. One only has to use the chronograph to measure the time required for any repeating event from start to end.
Then, where the second hand of the chronograph is stopped, read the measurement on the tachymeter that aligns with the second hand. That is your unit of measurement.
This may seem unclear, considering all the different units of measurement used for different activities. For example, how can it measure a car’s velocity in both miles per hour and kilometers per hour at the same time?
Well, it is possible because this tool, as odd as it sounds, does not rely on any unit of measurement. The trick is to ensure that any calculations done using it are performed using the same units.
In all situations or scenarios, if an action takes 25 seconds, the speed will always come up as 145. This may be 145 mph or 145 products manufactured in a production line in an hour.
The equation that is used by a tachymeter is as follows:
- T = 3600/t
Where T is the value on the tachymeter (the velocity), t is the time taken for an event to occur, and 3600 represents the number of seconds in an hour.
For example, if it takes 25 seconds for you to swing an axe (which would be highly unusual), it would mean that you make 144 swings an hour. You can use the tachymeter to verify this cause if you start the chronograph before swinging an axe and stop it right when you’re done, the second hand will line up with 144 on the tachymeter.
How to Calculate Speed and Distance
To measure the speed of an object or event, start the chronograph stopwatch when the object starts moving and stop it the moment the object reaches its destination. Wherever the chronograph second lands will determine its frequency per hour.
Best of all, the units on the tachymeter are entirely independent of any unit of measurement.
Let’s say it takes you 25 seconds to drive one kilometer. When you stop the chronograph after traveling a kilometer, the tachymeter will read 144. This will mean you are driving at 144 km/h (Slow down!).
If it takes you 25 seconds to drive one mile, then you’re driving 144 mph!
What Kind of Watches Use a Tachymeter?
Tachymeters are just about always paired with chronographs. Specifically, racing chronographs are standard, as they were designed explicitly for timing races, such as Le Mans, and have highly contrasting dials for easy reading when traveling at high speeds. They are also helpful for spectators interested in tracking the speeds of their favorite racers and for car enthusiasts.
Chronographs with this useful tool have also found a large market in aviation in both the aircraft and spacecraft industries.
How Do You Pronounce Tachymeter?
Tachymeters are fascinating tools found on some high-end chronographs. If you love watches, then you need to know how to pronounce this word! “Tachymeter” is pronounced ta-kee-mee-tuh with the accent on the first syllable (taˈkimətə(r)). According to the word’s etymology, it originates from the Greek word takhys which means “swift or fast,” and ‘meter’ which is associated with measuring.
The two terms most commonly confused with tachymeter are chronograph and tachometer.
What’s the Difference Between a Tachymeter and a Chronograph?
Although these words may be used interchangeably, they are quite different.
A chronograph is just another word for a stopwatch, while tachymeters measure both distance and speed. Typically, all tachymeters are found on chronographs, but chronographs can also be found without tachymeters.
What’s the Difference Between a Tachymeter and a Tachometer?
Unlike tachymeters, tachometers are tools that measure the speed of rotation in motors, machines, or engines. This is usually measured in revolutions per minute (rpm). You may have seen a tachometer next to the speedometer in your car.
Iconic Watches With a Tachymeter
Watches with tachymeters have now been used for over a century. Through the decades, many of them have become iconic because of the part they played in history, their designs, or exclusivity. In the following section, we will learn more about some of the most exciting and iconic watches that use a tachymeter.
One of the most well-known watches with this complication is the Rolex Daytona, named after the annual race in Daytona, Florida. It is designed for the most advanced racecar drivers and measures speeds up to 400 km/h.
The Omega Speedmaster is the watch that NASA officially issued to its astronauts for its missions to the moon. It is famous for being worn by the astronaut Buzz Aldrin, and it was the first watch on the moon in 1969. Although the tachymeter likely didn’t play a significant part in these missions, the chronograph certainly did. Notably, the chronograph was used to time mission-critical spacewalks.
Seiko 6139 Pogue
The Seiko 6139 is a significant part of space exploration history as well. The Japanese watch is also known as “The Seiko Speedtimer” or “The Seiko Pogue” after its most famous owner, the astronaut Colonel William Pogue who smuggled his Seiko 6139 chronograph onto the Skylab 4 mission without NASA’s prior approval. This made the “Seiko Pogue” the first automatic chronograph worn in space. Again, while the tachymeter probably didn’t play a huge factor in its usefulness in space, its chronograph sure did.
Bulova Lunar Pilot
Believe it or not, this is another certifiable “moon watch.” The astronaut David R. Scott wore the Lunar Pilot after the crystal from his Omega Speed master broke off during a moonwalk. The watch was designed for the Apollo 15 mission to indicate how long oxygen and other vital aspects, such as water and battery power, would last. The original watch that Dave Scott wore was a prototype.
Tachymeters are fascinating tools with a rich history and can be surprisingly helpful if you take the time to learn how to use them. Although considered obsolete, the feature is common in many luxury chronographs today, and kees the vintage racing watch charm going strong.