An 8085‐based microprocessor system was developed to monitor and control the magnetic field in a three‐axis, Helmholtz‐coil cage for an electron energy‐loss apparatus. The nulling field produced by the coils is monitored by three RFL Industries Model 101 magnetometers, and the coil current is provided by three Kepco PCX21‐1MAT power supplies. The computer reads the magnetometers and provides the appropriate reference voltage to each supply to null the field in each direction. The static field is typically nulled to 5 &mgr;G with this system.