Thermal neutron coincidence counters are used to measure plutonium-bearing materials in-line at the Plutonium Processing Facility at the Los Alamos Scientific Laboratory. Complicated operating procedures and time-consuming manual calculations have been eliminated by automating these instruments with a microprocessor-based control module. The instrument user performs several different measurements including the plutonium assay through a portable hand-held terminal that is connected to the control module. The results of a measurement are displayed on this terminal and can be transmitted to a central accounting computer. This instrument is programmed to perform all required calculations and store the results in the control module. These instruments have been readily accepted by operating personnel and their reliability and ease of use have contributed to the near-real-time nuclear material accountability system.