A comparator sense scan compares the plus input against a fixed minus input and includes the tie row so the output rail follows the stated decision rule. The 6 V equality row goes to the 0 V low rail in this ideal model; real comparators add input offset, bias current, hysteresis, rail limits, propagation delay, supply variation, noise, temperature drift, and voltage/timing measurement uncertainty.
A comparator decision table needs low, equality, and high sense rows before the output rail claim is trusted. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The comparator compares two voltmeter readings
The minus input is held fixed while the plus input is scanned. The equality row is included because this book defines a low-on-tie decision rule.
V+>V−⇒Vout=VHIGH
Three sense rows show below, tie, and above
The table makes the output rail a consequence of the comparison. There is no analog middle output in this ideal comparator model.
V+4V6V8VV−6V6V6VstateLOWLOWHIGHVout0V0V12V
Equal inputs use the stated tie rule
In the boundary row, both inputs read 6 volts. The output is the 0 volt low rail.
6V=6V⇒Vout=0V
Decision rows must be read before downstream loading
This scan stops at the ideal output rail. Output resistance, load current, hysteresis, and noise are separate budgets in later rows.