Autocalculate actuals units with Phisical % comp.

Goodafternoon at everybody!
Only one simply question...for you simply but not for me!
Is possible to autocalculate the actual units based on my phisical (then manual insert) % complete of activity an its budgeted units?
For example, if my phisical % complete of activity is 50% ad my budget units are 10.000 the actual units are 5.000.
I have tried all with only one autocompute system....about the schedule % complete of activity...
Are there any options...??!!
Thank you at everyone and sorry for my "basic" english!!
I Have Primavera P6

Mirko.