Re:speedo accuracy

[Pottree@domain.elided]

In a message dated 01/28/2002 10:36:55 PM Pacific Standard Time, 
owner-alfa-digest@domain.elided writes:


> At a true 60 mph, it takes 1.00 minutes to go one mile.  If your clock
> measures 10% less than that, you travelled the mile 10% faster, or 66
> mph.  10% more time means 10% slower, or 54 mph.  For what it's worth,
> my Alfetta comes up reading fast.  Indicated 70 mp really is about 66
> mph, according to calcs.
> 
First, I've used the milles bornes (mile marker) method to check the speedo 
accuracy of the 84 GTV6, the 87 75, and the 91 Spider as well as the older 
system on the 71 Spider.  The electronic speedos, when working (actually, 
mostly always) seem to be quite accurate on my examples; using a little 
simple math it also appears they are more accurate at midrange speeds and 
progressively less accurate at low or exciting speeds.  Of course, on all 
Alfas the most inaccurate speed is stopped.  I suppose this is an accuracy 
curve.  The mechanical system on the 71 which was broken a LOT of the time, 
was never accurate, but the degree and direction of the error is now lost in 
the mists of time.  I used the tach anyhow.

Now, suppose you find yourself with an electronic speedo and a good 
conneciton at the sender on a nice open stretch of road in a place where it 
is OK to drive like a maniac, such as Germany or Italy.  As you approach the 
speed of light, will the speedo be more or less accurate?  You won't be able 
to use the watch and road markings technique as time will slow down.  How can 
you calibrate it?

Stumped in LA
Charlie
LA, CA, USA

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