When I top up with fuel I generally put 20.00 litres in which is £23.78.
This annoys the wife something chronic because she puts £20.00 in, which is 17 litres or so.
I explained that when you buy a bottle of pop you don't buy £1's worth of pop you buy 2 litres worth of pop and pay the appropriate price like £1.09.
She doesn't get it.