The gauge can be made less random. If you remove the sender unit from the tank, take the aluminium cover off the float and carefully clean the two thin wires with some metal polish, reassemble and refit. That should improve things for a year or two before the wires need cleaning again.
I tried the resistor that was suggested by Richard but it didn't seem to make much difference. I don't think I would drive down to 0% indication and believe what is shown but it does give a reasonable indication of fuel level, I still reset the trip meter every refuel stop. The 280mm sender is a must or the tank show empty with almost half a tank of fuel left.
