Decimal Hour Time stopwatch?

[spinchb]

Hi All,

I was wondering if any of you know what a stop watch in decimal hour time would be used for? Someone gave me one 20 years ago and told me next time I saw him he'd tell me what it's for. I never saw him again! I have my theory that it's for timing auto rally races and converting easily to mph or km/h based on the decimal time. Anyone know for sure?

Thanks!
Shawn

[Led-Time]

This sounds interesting, can you post a picture...

[rewolf]

No idea, never seen one.
Sounds interesting.
Picture?
Are you saying this stopwatch displays e.g. 1.50833 for 1h 30min 30sec?

[spinchb]

Hi All,

Here's a link to a photo of it.

http://yfrog.com/0tzivydecimalhourj

Yeah, the time works as you suggest 30 min is .5 hour 15 min is .25, etc. It's a curious item!

Cheers,
Shawn

[Old Tom]

It's a rally stopwatch designed to make the use of a Curta mechanical calculator much easier (only a single H:M:S conversion rather than two in figuring out the problem)- a lot rarer than Curtas and probably very desirable to vintage rally enthusiasts.

[rewolf]

Hi All,

Here's a link to a photo of it.

http://yfrog.com/0tzivydecimalhourj

Yeah, the time works as you suggest 30 min is .5 hour 15 min is .25, etc. It's a curious item!

Cheers,
Shawn

Oops, I believed it was a digital stopwatch, but it's analogue

Do I understand correctly: the large scale is 0.010h (36sec) and the small scale goes up to 0.30h (18min)?
So this is not just a differently printed dial, but the movement too must be different from a "normal" stopwatch.

For convenience: direct link to photo

[rewolf]

@ OldTom: Is this true (designed for rallye and Curta), or just a guess, or even a joke?

[spinchb]

I think OldTom is right. I did a little math to test the idea.

For example:

If you're driving 3 km and it takes you 78 seconds, to get km/h:

(3 km/78 sec) X 3600 (this is the seconds in an hour)
= 138 km/h

In decimal time:

3 km/.02167 = 138 km/h

One calculation, all you need is the distance (odometer) and decimal time and a Curta Calulator and you know your average speed for a distance.

Cheers,
Shawn

[rewolf]

So if I want average speed in km/h, all I have to do is divide driven distance (in km) by taken time (in h)? That's ingenious ! Does this also work with miles?

AFAIK the Curta isn't exactly fast or easy to operate at divisions. A slide rule would be faster. But in both cases it's easier if the stopwatch tells you the time directly in decimal h instead of h:m:s.

[spinchb]

Yup, works with miles. Whatever your distance measurement is.

Cheers,
Shawn