The Tensimeter was developed to meet the need for a more dependable laboratory vacuum gauge which would be useful over the range of pressures from atmospheric down to a fraction of a millimeter of Hg absolute. The principle of operation involves using the boiling point of a pure compound as a measure of the pressure of the connected system. A description and calibration data are included. The advantages of the Tensimeter arise from the fact that it tolerates atmospheric water vapor which is usually present in petroleum distillations and causes other gauges to read incorrectly. It is small and convenient to use and does not require recalibration. It also produces an electrical signal which can be used for recording and control of subatmospheric pressures.