Quote:
Originally Posted by Vekke
5 readings of the average consumtion display for each measurement point distance from start. Not a instant readings. I believe that method is described in the other topics clearly enough with videos and all.
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OK, I also covered that in a previous post:
So I have been thinking about Vekke's (wrong) way of making measurements.
If I have it correct, in short he drives for 5.5km in one direction, then 5.5km in the other direction, car warmed up and on cruise control.
He takes readings from the car's average fuel (energy) consumption display at points along each direction. It appears these readings are taken at about 800 metre intervals.
These readings get numerically closer together (ie have less variation) as he proceeds in each direction, so he thinks the reading is becoming more accurate.
So let's look at a parallel. We're measuring maximum daytime temperatures in a room, over a week. In degrees C, the temperatures are:
M - 23
T - 24
W - 21
T - 25
F - 18
S - 19
S - 23
Now let's show the average at each point:
T - Ave 23.5
W - Ave 22.7
T - Ave 23.3
F - Ave 21.5
S - Ave - 21.1
S - Ave - 21.9
As with any averaging, the the trend in the cumulative average is less variation as the number of items in the data set increases.
But this data tells us nothing about the accuracy of the thermometer, or of other aspects that might be impacting measured temperature. For example, maybe on Thursday a cat slept on the thermometer!
So it's not the number of interim, cumulative averaging measurements which is important, it's - as has been said here many times - the distance over which the average is taken. (eg if we measured max room temps over 2 months, Thursday's cat wouldn't even be noticeable in the average.)
And, for anyone who has ever tested fuel economy, two runs in opposite directions of only 5.5km isn't going to be very accurate - at least, not when tiny changes are trying to be measured.
It would be interesting to see the variation with (say) 5 runs done in this way,
but with the car identically configured. Since in effect it's just the average of a 5km run (the interim points adding nothing to the accuracy) in each direction, I'd imagine the variation would be significant.
That's why no one else here does fuel economy runs over only 5km at 100 km/h.