This study describes the construction of a high vacuum station and the instrumentation and testing of two methods for obtaining the first derivative of the current-voltage characteristic of a Langmuir Probe, which is needed to determine the electron speed distribution in rare gases. The theory behind using a lock-in amplifier differentiator to obtain the derivative of the I-V characteristic of a Langmuir Probe is derived and discussed. A test was devised to check the instrumentation for correct operation. / M.S.