quartz oscillator varies with pressure as shown in fig1 next the display conversion circuit portion consists of a main amplifier 6 which further amplifies the signal from the amplifier 2 a rectifier 7 which changes the output signal of the main amplifier 6 to d c an inverter 8 which inverts the polarity of the output viltage of the rectifier 7 and a buffer 9 which biases the output voltage of the inverter 8 the bias level can be controlled by a variable resistor 9a the display may be either digital or analog in this embodiment it consists of a meter 10 pressure is read from the deflection angle of said meter the pressure characteristics of the resonant current of the quartz oscillator are such that said current increases as ambient pressure decreases as shown in fig1 therefore if the current at resonance is amplified as a voltage and is changed to d c to drive the meter the deflection angle of the meter will increase with decreasing pressure consequently the display will be the opposite of the detected pressure this is obviously undesirable from the common sense point of view therefore the inverter 8 inverts the polarity of the d c voltage and the buffer 9 then applies the bias voltage so that the meter dirving voltage shown in fig3 can be obtained in.