"Scott" wrote in message
news:46ae8308.426924174@localhost...
"Harry K" wrote in message
ups.com...

It is a useable instrument to detect what mode of driving is most
efficient even it it is not accurate. That is if it reports, for
example, 19 mpg over a stretch of road with tailgate down and then you
repeat the run in the same direction, same speed, same conditions,
etc. the reported mpg is then a useable bit of data. Yes, it will be
inaccurate but the comparison is useable and meaningful.

I would not assume that a faulty instrument is going to give me readings
that are inaccurate in a consistent way across a given range.

-Scott

Wait a minute Scott,

You got a little too ambitious with the clipping and the part you left in
was from a previous contributor. I only agreed that the errors in the fuel
computer would probably be consistent--electronics usually are--and then
recommended a proceedure to conduct coast down testing.

My contribution was the following:

"Probably true. However, the coastdown test mentioned elsewhere in this
tread is probably the most consistently reliable method--when properly
controlled. The most obvious requirements a state the coast down from
the same place and speed each time, record the remaining speed at the
seconde marker, continue testing in the same direction, warm up the tires
before the first test, and choose a day (or days) with constant temperature
and wind conditions. There are certainly more, but those are enough to give
a far more reliable result than any test in traffic that I can think of--and
even then, since we are discussing the drag of detached flow, the test may
only be valid for the speed(s) at which the test was run.

Peter"

Peter