According to the PMBOK® Guide, specifically the Monitor and Control Project Work process and Earned Value Management (EVM), the Schedule Variance (SV) is a quantitative measure used to determine if a project is ahead of, behind, or on its baseline schedule.

The Formula: The standard formula for calculating Schedule Variance is:

$$SV = EV - PV$$

(Where $EV$ is Earned Value and $PV$ is Planned Value).

The Components:

Earned Value ($EV$): The measure of work actually performed expressed in terms of the budget authorized for that work.

Planned Value ($PV$): The authorized budget assigned to scheduled work.

Interpreting the Result:

Positive SV ($ > 0$): The project is ahead of schedule because the value of the work performed is greater than the value of the work planned.

Negative SV ($ < 0$): The project is behind schedule because the value of work performed is less than what was planned.

Zero SV ($= 0$): The project is exactly on schedule.

Critical Path Context: While $SV$ can be calculated for any task, applying it to tasks on the critical path is vital because any negative variance there directly impacts the project ' s overall completion date.

Analysis of other options:

Option A and B: These involve Earned Schedule (ES) and Actual Time (AT). While Earned Schedule is a valid theory for measuring time-based variance, the standard formula for $SV$ in the PMBOK® Guide is based on $EV$ and $PV$. Furthermore, the formula for time-based variance is $ES - AT$, not the variations shown in A or B.

Option C: This is the inverse of the correct formula ($PV - EV$). Using this would result in a positive number when the project is behind schedule, which contradicts standard Earned Value logic where positive always equals " good. "

Per PMI standards, the most common and accepted way to communicate project performance relative to the schedule baseline is by calculating Earned Value minus Planned Value.