A sensitive differential mercury manometer is described. Mercury surfaces in two arms of the manometer form plates of condensers connected to two nearly identical oscillator circuits. A change in pressure produces a change in the beat frequency of the oscillators which is measured by comparison on an oscilloscope with the output of an audiosignal generator. For 0<&Dgr;p<0.02 cm an accuracy of 0.1 to 0.2 micron of mercury is obtained. For &Dgr;pbetween 0.02 cm and the maximum measurable with the manometer (approximately 0.25 cm) the accuracy appears to be 0.1 percent or better.