Don't believe everything computers tell you!

[Orcade-Ian]

Thanks for coming to my rescue folks, especially Nurse Julie, I foolishly thought that with all of this VW stuff about, I might get others to sit up and take notice and question some of the info we are bombarded with.
Without wishing to 'do anyone's head in' , another observation during over 100,000 miles of riding GoldWings, about 20,000 of which were in the Netherlands, Germany, Austria and Switzerland,
the fuel consumption is always around 10% better than in GB. No, I don't carry extra weight or deliberately have a fuel leak when using the bike in GB

One positive outcome from this post is that I have now donated!!

For James, With only a handful of filling stations in Orkney, I filled up at the same one before and after, even used the same pump so the car was in the same orientation and filled to the brim but having used 230litres of fuel for the trip a few cc's would make no real difference.

Ian

[Johnwebley]

maybe I am reading between the lines something that is not there !

 but I have my standard 500, fuel capacity 14 ltrs,

 a few weeks ago I filled it with 14.1 ltrs of basic Shell,

 how accurate are the pumps ??

[totty]

Pumps often have a label stating the tolerance and/or the temperature that it was calibrated at.

[Bullit]

I understood your post from the first time reading it. Now I would say a 6% indifference would be well within an acceptable tolerance. Also as fore mentioned there is a possibility of upto a 10% tolerance on the speedo so the trip computer in my opinion is fine. Also you said the garmin showed 2960 miles and that's what you worked out your figures with. But how many miles did the car display? If it was less due to an incorrect reading then this would affect the result.
And one statement worried me with the whole scientific process "A small discrepancy would be insignificant", the computer doesn't have insignificant in its programming.

Not having a go just a healthy debate lol

[ka-ja]

Hi,
    Nonsense in-nonsense out!

[SteveD CB500K0]

My turn...

I work in IT and have been programming for 40 years.

Computers don't make mistakes.  They merely perform calculations on given data according to the programme.

In our Tech Support office, we get customers who insist that the computer is giving the wrong results. We ask them what they have changed. They inevitably respond "I haven't touched it"... 

We have an (internal) response to this: "PICNIC"

Problem In Chair, Not In Computer.

[SteveD CB500K0]

    Nonsense in-nonsense out!

That's the polite version...

[ka-ja]

  *We have an (internal) response to this: "PICNIC"*

     That  is also polite according to my experiences, something like "operator error"

[Dave_Canada]

The GPS distance traveled function has some built-in inaccuracy. Position is calculated continuously but that takes a while. On a curve, the sequential calculations are joined with straight lines to measure distance. For infinitely small line segments, the calculated distance is equal to the true distance. Your GPS doesn't create infinitely small segments. Over a 3000km trip this will underestimate the total distance by a bit unless you have a 1500km straight road. Also, most GPS units ignore altitude. Climb a 30 degree hill between points 10 km apart on the map, and GPS will say you went  10km but an accurate odometer will read 11.5km.
Your car's odometer based on wheel rotations (and any fuel calculations based on it) will never be exact - tire wear & pressure and vehicle load changes affect the tire diameter and odometer result. Your GPS will always under-report distance traveled unless you travel on dead straight and dead level roads, inflating fuel mileage calculation.
A 6% error is not bad. Car speedos are generally optimistic by a few percent.