oil

1 litre additive here – 16,90
Heizöl Additive

5000+4508 litre = 9508 litre

1367,67 – brutto for 3000 litre

2127,47 totally
38,31 / 100 litre x 3000
42,34 / 100 litre x 1508

at the moment tank display shows >9200 litre totally, before tanking it was exactly 5000 litre, so the difference is 4200 litre. Tanking was 4508 litre, so there is an error of 308 litre.
up to 2 litre additive added, one litre is for 2000 litre.

38,31*30=1149,30
42,34*15,08=638,49
+=1787,79
+19% 339,68
=2127,47 OK, perfect.