OK, thats normal for your first tank (the error I mean).
The Scan gauage initially just uses a standard 3.0 Litre figure for injector flo rates and it works out fuel used by "standard fuel flow x how long the injectors are open". When you adjust the amount of fuel you add to the tank at your first fill that + or - which shows as a percentage in your adjustement is how much the Scanguage will recalculate with so it will now be "standard fuel flow/percentage correction x injector cycle".
IE if the vehicle takes 5% less fuel than predicted the Scanguage will now deduct 5% from the calculations of fuel flow and fuel used etc and from now on the AVG and LPH figures should be much more accurate. Another fill or two and you will not need to touch it again.
Resist the urge to change that % figure every fill... if the fill is within about 2 or 3 litres per 100 of what is expected those small differences will only have you chasing your tail. Only adjust it if the figures are out consistently one way IE always takes more fuel or always takes less.
You may get the odd "weird" figure if you do a tank full of work out of the norm. Say, a hell of a lot of lo range slugging you normally wouldn;t do whilst on Hols at the beach for example. Again, don't adjust the fill up figure. All you are doing is putting in an error for the next tank useage which will be back to normal.
I normally take on 120 to 150 litres at a time and the Scangauge is normally with 1 or 2 litres either way BUT has on two occasions been out by 6 and 11 after some really hard yakka and a 1,000 K hi speed run out back of WA.
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