On 07/22/2017 6:42 PM, Mad Roger wrote:
....

The main point for bringing up the otherwise unrelated issues of
speedometer accuracy and repeatability is that some people here seemed to
think if they ran a calculation more times, that the "accuracy" somehow
(magically?) gets better because (magically?) their reading is low as much
as it is high.
....

NO! That is not at all what any of those people said. You're simply
repeating the same contention which is ok as far as it goes in that a
point estimate is not the same as averaging or using other techniques to
increase the precision of the measurement.

They (and I in particular) only point out that averaging muddles out the
differences in intermediate filling levels.

The alternative measurement increases the denominator in the computation
at the expense of no additional error in the measurement of the quantity
used; the errors in the intermediary quantities in levels cancel
identically because all the fuel gets used and the final level
discrepancy is only the one but is is now related to the total quantity
instead of the single.

There has been nobody I've seen who's claimed a bias error will be
anything but that -- but in this case that one is a simple calibration
and correction that will not add appreciable error if made. And even if
not won't have any bearing on differences in performance over various
driving conditions for the same vehicle in terms of seeing changes in
that vehicle's relative performance. That it is off by whatever that
percentage in mileage is from the actual is too obvious to belabor and
nobody here has made any claim to the contrary.

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