of fuel to the tank a fuel tank level signal is generated by a conventional float operated gas gage tank unit 22 in the fuel tank of automobile 12 in fig1 the fuel tank level signal may be stored in a non volatile ram each time the engine ignition switch is turned off each time the ignition switch is turned on the value of the prevailing level signal is compared with the stored value if the switch on value is significantly larger than the switch off value it is assumed that fuel has been added to the tank and this new 34 filled level 34 is stored in non volatile ram until the next time fuel is added to the tank each time a new filled level is stored a reset signal is sent to the counters 78 80 82 and 84 shown in fig5 this reset signal stores a value in the counters midway between the values of predetermined constants 34 b 34 and 34 c 34 in one embodiment according to the present invention when the prevailing fuel level is higher than one quarter tank below the 34 filled level 34 the system will decide that there has not been sufficient experience to evaluate the appropriateness of the newly added tank of fuel in such a case if a fuel evaluation is requested decision.