On the PMP certification exam, you'll see five to ten questions on variances and indexes. Here's fundamental information that project managers need to determine cost and schedule variances and indexes.
For variance and indexes, always start with EV.
When looking for information on schedule, use PV.
When looking for information on cost, use AC.
For a variance, subtract.
SV = EV – PV
CV = EV – AC
Negative is bad; positive is good.
For an index, divide.
SPI = EV / PV
CPI = EV / AC
Less than 1.0 is bad, greater than 1.0 is good.