screw heads the wires 73 and 75 lead to the circuit 8 which is conventional in design the circuit 8 includes a first portion 77 that contains an integrated circuit lm1042 manufactured by national semiconductor corporation and called a fluid level detector by the manufacturer a second circuit portion 79 includes a ba656 monolithic integrated a signal level and display circuit manufactured by rohm corporation the circuit portion 79 includes a number of light emitting diodes 81 83 85 87 and 89 which are turned on in correspondence with the measured liquid level a calibrated volt meter not shown could be used to indicate the liquid level in correspondence with the output signal from detector 72 in operation the circuit portion 77 drives a steady state current through the probe wire 53 thereby causing the wire to heat up if the wire is surrounded by air ie the wire is not immersed in the oil 3 the wire will heat up rapidly and cause the wire resistance to change by a relatively large amount on the other end if the wire is fully immersed in the oil the oil will absorb the heat and keep the wire at approximately a constant temperature varying amounts of wire immersion in the oil.