For every set of input vectors that are applied at a particular time ("tA"), the output logic levels used for comparison are determined by finding the time of the next transition on any input vector ("tB") and taking the output levels that existed 1 ps prior to that transition time. In other words, tA outputs are checked at tB - 1 ps.

The functional comparison rules govern the comparison of expected versus actual outputs displayed in the Simulation report, as well as the Compare to Waveforms in File command (View menu).