# Very specific vintage tachymeter - what is it for?



## Mechaniker (May 26, 2017)

Can anyone help me to identify this?

I find it intriguing because it is a single-purpose watch, and I wonder why it was ever built.

It is a tachymeter. The single hand takes only 18 seconds per rotation. The dial is clearly a tachymeter, and it also reads 'm/sek'.

I found that is measuses speeds of 60 to 500 km/h, with the highest accuracy between 60 and 150km/h.

As such it seems to be made for cars.

You start the watch and 300m further you stop it, and it displays the speed in meters per second.

It runs well, mechanism is clean - and it even has a small compartiment with spare parts. It has only one inscription, the number 95225. That's it. No brand name, nothing.

Here's my question: Why 300m? What could be so important to design and build a specific watch for measuring speeds over 300m ?










And one more of the inside:

http://i293.photobucket.com/albums/mm62/Puckaneer/IMG_20170526_111216.jpg


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## Chromejob (Jul 28, 2006)

Wow. I'm intrigued…


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## Caller. (Dec 8, 2013)

I used the image to search on the net and came across the OP's thread on a Dutch site about the same watch - it was the only page with a matching image!

http://www.horlogeforum.nl/t/wie-weet-waar-dit-vandaan-komt-hele-specifieke-tachymeter-snelheidsmeter/109040

Very interesting answers to the original question - google translate is your friend!

It is fascinating and are you any nearer to a true answer? It was obviously made for a very specific purpose.

Do you know when, where and who it was made by?


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## Chromejob (Jul 28, 2006)

I see noting to indicate it is specifically for timing vehicles at speed. Couldnt' it be used for timing other high speed revolutions?


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## William_Wilson (May 21, 2007)

It appears to be metres per second, so it covers from 540kph to 61.2kph. these are conventional engine aeroplane velocities.

Later,
William

Post script - I'll add, for the sake of clarity, relative to the age of the timepiece.


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## Always"watching" (Sep 21, 2013)

Thanks William.

As a stop watch fan, I absolutely love that watch, mechaniker, and I find it frustrating that there is no indication of the maker or any other identifying marks.

The link established by William with aero engines is fascinating, and I believe that the technical term for this sort of watch is a "velocimeter." I have now read that there are a number of similar watches with different timescales for different purposes, and evidently these also are subject to debate about their exact purpose.

Thanks to this thread for opening up an interesting sideline on my stopwatch collecting.


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## Mechaniker (May 26, 2017)

Caller. said:


> I used the image to search on the net and came across the OP's thread on a Dutch site about the same watch - it was the only page with a matching image!
> 
> http://www.horlogeforum.nl/t/wie-weet-waar-dit-vandaan-komt-hele-specifieke-tachymeter-snelheidsmeter/109040
> 
> ...





> Thanks!
> 
> That was my post, and my photo. I'm Dutch, so I tried my luck on a local forum as well.
> 
> ...


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## Mechaniker (May 26, 2017)

> Thanks William.
> 
> As a stop watch fan, I absolutely love that watch, mechaniker, and I find it frustrating that there is no indication of the maker or any other identifying marks.
> 
> ...


 Thanks!

I am a stopwach fan as well! That's why I recognized this and bought this. The round-time still boggles me, as it's not a regular stopwatch with just a strange dial. They really went out and built a 18 second timepiece. That makes it totally single-purpose.

So far no-one has recognized it yet, which in the age of the Internet is a Very Strange Thing.

As Alice would say: Curiouser and curiouser.

I have not yet exhausted all my options and I will keep searching. Thanks very much for your interest!!


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## Mechaniker (May 26, 2017)

William_Wilson said:


> It appears to be metres per second, so it covers from 540kph to 61.2kph. these are conventional engine aeroplane velocities.
> 
> Later,
> William
> ...


 Hm, that makes it fit for aeroplanes, you recon?

Bear in mind that at the upper end of the scale it is very imprrecise. One second (!) makes the difference between 100 or 150 meters per second, which is a 50% deviation. Even a tenth of a second is already 5% inaccuracy at those speeds - almost impossible to achieve with a manually operated clock!

At the mid-end, one second makes the difference between 32 or 30 meters per second (about 6%) and at the lower end it, an error of a second means you measure the speed 0.5m/s wrong - only 3%.

So while it can technically be used up to 540kph, it is highly inaccurate at measuring that speed. Accuracy comes at at speeds around 150kph down to 70. Any slower than 70 and you run the risk that the thing you're measuring is going too slow and it crosses the 18 seconds boundary.

So while we are indeed talking about a maximum scale of 540 to 61.2, a reasonable / usable range is more 150 to 70khp, according to my reasoning. That can not be aeroplanes - it can't be bikes. Can't be boats. Possibly model airplanes, otherwise it has to be cars or motorbikes.

Thanks for the feedback, though!.


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## Mechaniker (May 26, 2017)

Chromejob said:


> I see noting to indicate it is specifically for timing vehicles at speed. Couldnt' it be used for timing other high speed revolutions?


 Two things indicate this. It says 'm/sek' which means 'meters per second' in German. And look at the scale: The inner circle is seconds. The outer scale is meters per second when you measure the time something takes to travel 300 meters.

It measures top speeds of 540 kilometers per second but very inaccurately - see my other post. It is pretty accurate at speeds between 70 and 150kph - and I don't know anything at those speeds except cars and motorbikes. Planes = too fast. Bikes, walkers, boats too slow.

Thanks for the very interesting feedback, though! I am not much closer, but I like a bit of a puzzle!


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## Always"watching" (Sep 21, 2013)

I am very intrigued by these velocimeter stopwatches, and I shall be on the lookout for one to fit into my collection. I shall also do more research on this subject, and I am sure other members will be able to fill in any gaps with info I discover so that we can find as complete picture.


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## lebaron (Mar 8, 2009)

Nothing but guessing, but I am wondering about other engineering applications: maybe how far a float in a water filled pipe or gulley travels, to calculate volume over time, or fuel flow. Maybe cable laying from a vessel?

Looks to be a well engineered movement.


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## bridgeman (Dec 9, 2008)

I make a wild stab at something to do with the relationship between 2ww aircraft gun cameras and film speeds.

spitfire armament seems to have given a maximum of 18 seconds fire power before ran out of ammunition and presumably German aircraft about the same?

Bursts would have been much less say 4x5 second bursts.,somehow gun camera film speeds had to be synchronised .........

i cant do the math as our USA friends say but could it be a possibility?


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## Karrusel (Aug 13, 2016)

bridgeman said:


> I make a wild stab at something to do with the relationship between 2ww aircraft gun cameras and film speeds.
> 
> spitfire armament seems to have given a maximum of 18 seconds fire power before ran out of ammunition and presumably German aircraft about the same?
> 
> ...


 :thumbsup:

Is your real name 'John Nash'.....?


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## Mechaniker (May 26, 2017)

Thought it would be nice to send an update.

A colleague of mine knew the answer!

It is a nurse watch. Start the timer, count five heartbeats, and the tachymeter indicates the hearth rate (standard 60 per minute).

Cool, I never heard of this before.


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