I think that this over simplifys the situation. Yes the non-linear thing make the unit less useful. If you connect the unit while out of the tank (connect it to the wire at the tank and ground the unit) you can get someone to sit in the car and you can move the arm to see how it reads on the gauge. By bending the arm you can adjust where it reads. This doesn't fix the arc of the reading but can change what the gauge reads in the the critical area. If you start the process with the amount of gas that you want in the tank when the gauge reads E, then you can adjust it to read that by inserting the unit and holding it in place an then seeing what the gauge reads and adjusting the arm. It might take a few trys to get it where you want it. Yes this really isn't something you can do without a helper, but all that person need to know how to do is read the gauge and yell to you.
