The frequent use of Langmuir probes in the determination of electron temperatures and number densities in plasmas makes it desirable to have rapid methods of data reduction. This paper describes a simple and accurate instrument for carrying this out without the necessity of using logarithmic amplifiers or oscilloscope displays. Apart from its advantages in ease of construction, its calibration is particularly simple and drift‐free. In operation, the device samples the probe characteristic at two values of current, and yields a numerical value for the electron temperature on a meter. Linearity of the characteristic is examined by varying the sampling currents. Provisions are made for ion current to be compensated and measured, and for the electron saturation current to be estimated.