An improvement to a system for measuring (a) the voltage level of a waveform at a specific time with respect to a reference point in time, (e.g., clock or sync pulse) and (b) the time required with respect to a reference time for a waveform to reach a specific voltage level. In the first case, the voltage at a given sample time is measured, while in the second case, the time to a given voltage is measured. The system incorporates a go/nogo decision circuit which determines if the characteristics of a circuit under test satisfy certain reference criteria. The go/nogo circuit comprises a discriminator which examines a test signal for both amplitude and time. The discriminator compares the level of the input test signal with a reference signal at the time of strobe occurrence. The condition of the discriminator is monitored by a detector circuit which further passes this condition on to a voting logic which makes a go/no-go decision based on a plurality of samples.