Abstract: Testing apparatus monitors signals at selected test points in a tested device. An operator specifies sets of signals defining a display window during which all signals at the selected test points will be available to the operator for immediate or later examination. One set of signals defines the beginning of the window. Another set defines the end of the window, but only after other sets or conditions, also specified by the operator, occur. For each set, the operator specifies test points monitored, signal states expected and what happens when the expected states occur.

Abstract: Signals at selected points on a test device place indicia on a record indicating, for each selected point, a selected logical active level and an initial polarity level. At preselected time intervals, levels, level changes and the number of transitions per change appear on the record as human-readable symbols. Each selected points signals are translated into digital representations which are stored for comparison with subsequent digital representations from the point. Counters record the number of changes thus detected and provide to the record appropriate symbols depicting the pre-change value, the number of changes and the post change value.