A cost effective approach to accurate, automated Gaussian beam diameter measurements is described. The measurement system uses an inexpensive computer and interfacing to a moving slit beam scanner. The software is written in Basic and machine language. The choice of using either language at any point of the program is based on tradeoffs between speed and instruction compactness in memory. The operator is allowed to make other tradeoffs at data taking time. The algorithm, which interprets intensity data from the beam scanner, gives a beam diameter measurement that is invariant to ambient light and d.c. offsets in the electronic circuitry and is relatively immune to noise. Factors that influence the choice of program flow and hardware configuration are discussed. The choice is optimized for an operator who expects fast, reliable and accurate measurements from a simple and inexpensive measurement system.