what a fookin con lol.

There is a service mode you can put the car into to check read out's from the engine, ecu etc. to enter it you hold down the trip reset button and switch on the ignition and then after about 5 secs release the trip button and the car is in service mode. press the trip button to cycle throught the dash test mode and the read outs i.e water temp, oil temp, oil pressure, battery voltage, ecu hex reading, fuel gauge calibration.

The fuel read out isnt mpg its just a reading off the fuel tank sensor i think it reads from 256 (full) to 0 (empty) used for checking calibration.

BTW i just i just saved you a £1