Average rating calculation in appraisal form

Hi Experts

I have created Appraisal form where my template contain KPI & Management Competencies as well technical Competencies.

Now , there is rating scale is like this 1=Below Satisfactory, 2=Satisfactory etc.

there will be average rating on reporting officer for all the Competencies

exm-

KPI Rating

KPI1 3

KPI2 2

KPI3 4

Now average rating = (3+2+4)/3=3

Similar way , there will be average ration on Management Competencies as well technical Competencies

i need to get final rating in this way

Final rating(FAPP)=

(average rating for reporting offier-on KPI+ average rating for reporting officer on Management Competencies+ average rating for reporting officer on technical Competencies.) divided by 3.

I want to use badi - HRHAP00_Vel_Det for this calculation.

Kindly suggest me , how to go about it.

Note: There is no Weighted rating here.

Thanks

Anwar