As below!Are you working it out on the £20 quid you put in or the 20lts you put in.Put in twenty quid this week and twentyone quid next week and so on and you will find the gauge always returns to the same fill mark,probably nowt wrong with your car(though you don't give ANY details)try filling in private millage on your tax return and you will see if you are using a lot of fuel...paying a lot for it more like.Happy motoring.