What is the Schedule Performance Index $($SPI$)?$

Figure $1$: You have a project to build a new fence. The fence is four$-$sided as shown. Each side si to take one day to build and is budgeted for $$1,000$ per side. The sides are planned to be completed one after the other. Today is the end of day three.

Key: S$=$ Actual Start, F$=$ Actual Finish, PS$=$Planned Start, PF$=$Planned Finish

Activity Day $1$ Day $2$ Day $3$ Day $4$ Status End of Day $3$

Side $1$ S $---------------$ F Complete, $$1,000$

Side $2$ S $-------------$ PF $----$F Complete, $$1,000$

Side $3$ PS $------$ S $-------$ PF half complete, $$600$

Side $4$ PS $---------------$ PF not yet started

Group of answer choices

$\mathrm{.}83,$ which is behind schedule

$1\mathrm{.}2,$ which is behind schedule

$\mathrm{.}83,$ which is ahead of schedule

None of the above