antedeluvian--we had similar needs for using HP/Agilent network analyzers on production lines. the HP boxes were easy to control over IEE 488 (GPIB) using an interface card in a standard PC. Then we controlled when to make a measurement by the PC, with a GUI. The data all came over to the PC and were analyzed for pass/fail criteria against stored return loss profiles for reference devices. So in effect the instrument becomes virtual like Martin says, and it is up to the test engineers to make sure their code is right.