POTENTIOMETER and bridge-balance systems using galvanometer detectors and electromechanical amplifiers have been used successfully in the recording of industrial process variables for many years. Electronic detection and amplification has greatly extended the field of application of these basic instruments by increasing response speed, sensitivity, and range of application.1, 2 The versatility and standardization of design made possible by the electronic servo amplifier has permitted the utilization of the accurate null-type metering system to the continuous measurement and control of practically all process variables which can be converted to electrical functions. The electronically operated null-balance recorder is admirably suited to perform as an analogue calculator, and circuits and devices are available which permit the computation of derived process variables including sums, differences, products, ratios, powers, roots, and trigonometric functions. The electric computing systems offer numerous advantages over equivalent mechanical methods. These include: 1. Transmitters (also called transducers or pickups) whose outputs are to be included in the calculation can be located remotely from one another in their most favorable location relative to process. In this way the electric system offers the additional advantage of short-range telemetering for centralized process control. 2. Complete electronically operated computing systems are built up using the basic standard components of the simple measuring systems. Mechanical computers generally require special design of linkages, cams, and gears. 3. Functions can be computed accurately over wide ranges and with relatively straightforward calibration procedure. Mechanical computers involving complex linkages and cams are generally limited and require special calibrations for each application.