That is correct, $10 is not 17.50 guilders. I look at the pump, divide by 2 and add 10%, simple and easy. So if I want $10 dollars, then that should be approx. working backwards at 21.00 guilders. So when asking for $10 dollars, what you do is double (for 20) and add 10% of the dollar amount (for 1). That will get you close enough. For just $10 maybe the 17.50 is simple and easy. I never get $10 in gas, generally $20 at the min. based on how many days we have left and what I have use to that point.

Think the last time I got $10 was the last trip, used more at the end than I thought, so was making the tank right, knowing that $10 was too much. But was not interested in asking for $8.50!

NO the above is not right. Too much. Closer is 9 plus the 10 percent to equal the original $10) meaning $9 plus 90 cents. Easier doing it the other way.

I just look at the guilder price, knowing the formula and if it is close then done. So far never have felt that we overpaid. But do always look at the price on the pump, but do that at home also.