Thursday, January 20, 2005

Tachymeter Instructions

I found some good instructions for how to use a tachymeter scale on a chronograph from
Q. What is a TACHYMETER (TACHYMETRE) scale and how does it work?


The tachymetre scale can be used to compute many things, but it's primary purpose is to compute the speed after noting how long it takes to travel a fixed distance (e.g. one mile or kilometer). The dial is a scale which computes the function: Tachymetre Dial = 3600 / Elapsed Time in Seconds

The scale is valid for all elapsed times from 7.2 seconds to 60 seconds. If the duration of the event is outside this range, then the answer on the dial is invalid.


For example, suppose you wanted to measure the average speed a racecar was traveling. After starting the chronograph function when the car passes the starting line, and stopping it after the car travels exactly one mile, you note that the chronograph hand is pointing at the 4 o'clock position (i.e. 20 seconds have elapsed) Looking beyond the 4 to the Tachymetre dial reveals the chronograph hand pointing at 180. This means that the average speed of the car would be 180 MPH.

Let's say, instead of the race car speed, you are measuring something much slower, like sailboat speed. In this case, you need to use a shorter distance because the elapsed time must fall within the 7.2 - 60 seconds range. For this example, let's say it took 36 seconds for your sailboat to travel 1/10 of a nautical mile. Reading the tachymetre dial gives a speed of 100 knots. However, since we only traveled 1/10 of a nautical mile, the actual answer is 1/10 of that or 10 knots.

Now let's say you wanted to measure the speed of a VERY, VERY fast airplane: after traveling 10 kilometers, you noted that 10 seconds have elapsed. The tachymetre dial gives an answer of 360 but we traveled 10 Km. Therefore, the answer is 10X360, or 3600 km/hour.

There is really nothing magic about using the Tachymetre dial to measure speed. You can also use it to measure other things, like gas consumption. Suppose it took 50 seconds to burn up a gallon of gasoline. Reading the tachymetre scale shows that you are burning 72 gallons of gasoline per hour



Anonymous Anonymous said...

finally something i can understand.

ive been trying to understand what a tachymeter does, and now i can apply it to real life

thanks alot

February 02, 2008 11:36 AM  
Blogger Steven said...

That's great i went watch shopping awhile back.The sales lady had no idea how to use the tachymeter. just a fancy dial, she said. its for looks.

April 11, 2008 10:41 AM  
Blogger Malgados 5 said...

Thank you for the clear explanation to estimate speed and for the final example illustrating how to read on the tachymeter any sort of rate over time.

April 13, 2008 9:20 PM  
Blogger chetan said...

thanx man the information was really usefull ...

July 18, 2008 12:03 AM  
Anonymous Anonymous said...

A great and easy to understand explanation. Thx! KM.

September 13, 2008 1:39 PM  
Anonymous Anonymous said...

That was LUCID,Thanks

September 22, 2008 6:55 AM  
Anonymous Anonymous said...

That's what i needed. Thanks a lot.

January 12, 2009 2:30 AM  
Anonymous David said...

Exactly what I was looking for. Well said so that anyone could understand. Thank you.


January 23, 2009 5:00 PM  
Anonymous Anonymous said...

This comment has been removed by a blog administrator.

February 03, 2009 1:33 AM  
Anonymous Anonymous said...

so it turns out that the tachymetre is completely useless u dont require a tachy to tell u that if a race car traveled 1 mile in 20 sec its speed is 180 mph. its obvious that it is 3 miles per min n obviously 180 miles per second. its for dumbos who cant calculate this bit. Its a fancy dial after all.

March 29, 2009 9:29 AM  
Anonymous Anonymous said...

180 miles per HOUR dumbo...

March 30, 2009 12:13 AM  
Anonymous Anonymous said...


Yes, you CAN calculate this in your head, but this is a tool you can use to free up your mind and concentrate on driving that get-a-way car.

After I get done laughing and wiping the beer off my screen & keyboard, I just want to say thanks for the explanation!

May 01, 2009 5:30 PM  
Anonymous Anonymous said...

I wonder what the March 29th poster was doing here in the first place.

May 01, 2009 5:32 PM  
Anonymous Anonymous said...

We always Wow Power Leveling and world of warcraft gold

July 07, 2009 8:40 PM  
Anonymous 2k4_8 said...

I just did quite a bit of reading and this is the best one that I have found for letting me actually visualize and understand how to use one. Thanks for posting this!

August 15, 2009 3:57 PM  
Blogger namael said...

Dude... Thanx a span for taking the time to save us the hassle of looking up the purpose and function of the 'fancy dial' was. Now i understand wat it is. But how would one calculate how fast a snail is travelling? Good question huh? Thanks again

August 16, 2009 5:17 PM  
Anonymous Anonymous said...

can your units for the snail instead of mph use fps feet per second or feet per hour or cm per hr

September 03, 2009 7:31 PM  
Anonymous Anonymous said...

The miracles of the tychmetre on my watch is now over due to the given instructions though I'm not clear why the plane speed on the example can't be excuted directly i.e. It need calculation. But it is enough to say thank you indeed.
Lusenga - Tanzania

October 14, 2009 1:35 AM  
Anonymous Anonymous said...

thanks alot
very useful and clear.

October 24, 2009 4:48 AM  
Anonymous Veeling said...

that's great!

May 16, 2011 2:19 AM  
Anonymous Anonymous said...

Thanks a lot, now understood whats the use of the tachymeter.
Clean explanation

June 07, 2011 3:59 AM  
Blogger #1steelerfan said...

that wass great info and helped alot thanxx!!!!!!!! ;)

July 31, 2011 3:23 PM  
Blogger #1steelerfan said...


July 31, 2011 3:25 PM  
Blogger thathu said...

a very good answer addressing the query fully.i had a vague idea only about it. now very clear thank you .now many will understand tachymeter and also that it is not ornamental alone thanks

October 24, 2011 8:59 PM  
Blogger thathu said...

a very clear x'planation. now every one will know what it is&its uses .and that it is not ornamental only!! thanks

October 24, 2011 9:02 PM  
Anonymous Anonymous said...

Finallyyy a answer that makes 100% sense thank youu

December 15, 2012 3:58 PM  
Anonymous Anonymous said...

With the reference to
Tachymetre, there is a supplementary information that the limitation of the tachymetre is from 7.2 seconds to 60 seconds. Any elapsed time outside that range will have a invalid result.

February 13, 2013 10:59 AM  

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