OK, fair enough. Here's how you calculate the SPI, from scratch:

SPI = EV / PV (Earned Value / Planned Value)

in other words,

SPI = BCWP / BCWS = Budgeted Cost of Work Performed / Budgeted Cost of Work Scheduled = (Total Budget * % Complete Actual) / ((Hourly Rate or Daily Rate) * (Number of days scheduled or Number of hours scheduled))

%Complete Actual = AC / EAC Where AC is the Actual Complete and EAC is = AC + ETC. ETC is the Estimate To Complete.

%Complete Actual = AC /(AC + ETC)

In any project we have AC and we have ETC

So now the SPI formula is:

SPI = (Total Budget * (AC/(AC + ETC)))/(Hourly Rate * Number of planned hours)

Here's an example, assuming you have a project with a total budget of $100,000. The project consists of 10 tasks (usually it's work packages but let's keep it easy) of equal lengths, each is a 100 hours, and each hour costs a $100. Let's assume you look at your baseline, and you see by now you should have finished, by now 5 tasks, but in reality, you only finished 4.

Now your PV = 5 tasks * 100 hours (for each task) * 100 = 50,000

Now the actual cost is AC = 4 tasks * 100 hours * 100 = 40,000

%complete = AC/(AC + ETC) = 40,000/(40,000 + 60,000) = 40%

Now the EV = $100,000 * 40% = 40,000

SPI = EV / PV = 40,000 / 50,000 = 0.8. Since SPI is below 1, this means that we are behind schedule, and it is taking us 10 hours of actual work for each 8 hours of planned work.

I was going to give you another example, but it was very complicated, so I dropped it.

Anyway, hope the above helps!