SPI and CPI

Hi

I am facing problem in one situation in a project. activities are so huge in my project i cant mention here therefore i am using a dummy project having two activities to illustrate my problem.

Activity Name        Original duration(Planned)   Planned units                Actual Durations           Actual Units    

Start                          05days                                      80hours                      06 days                           100hours

Finish                         05 days                                      80 hours                     07 days                           100hours

For first activity is 1 day late it completes in 6 days and in 100hours. When i have put my actual and view my result in tracking at end of first activity it shows

SPI = 0.85 (behind schedule) CPI = 0.8, after end of first activity with second activity actuals not put in yet

thats ok fine

but when i put my actuals of 2nd activity it completes in 7 days & 100hours and at end of second activity i get following values

SPI = 1.00 , CPI = 0.82, after end of second activity

Now my boss says go back to the end of first activity and tell me wht was SPI and CPI , I took my Data date to after end of first activity and got following results

SPI = 1.61  CPI = 0.82, after end of first activity with second activity actuals on

Now my question is that why above  values (SPI = 1.61 , CPI = 0.82) are not matching with the  first values (SPI = 0.85 , CPI = 0.8).

I am using percentage complete type = duration

Regards

Planning Guy