On each side of a thin diaphragm, separating two chambers, a condenser plate is mounted at a small distance. The two capacities thus formed are part of a bridge circuit which is fed by a high frequency oscillator. An amplifier with a narrow band width and a phase - dependent rectifier give a voltage which is fed back to the manometer. At one side of the diaphragm a pressure prevails, much lower than the one to be measured, at the other side the gas is admitted, the pressure of which is to be measured. The displacement of the membrane by the gas pressure is almost completely compensated electrostatically by the feedback voltage. By virtue of a differential way of feedback the reading is proportional to the pressure. The range is from 10-5-0.5 mm of mercury pressure difference at any absolute value. The apparatus is made of chemically fairly resistant materials, and as its indication is in principle independent of the nature of the gas, it can be used for almost every gas. The apparatus can also be used as a non-direct reading instrument in which case the upper limit of the range is 1 mm of mercury.