Use of Costing Variant Actual (PPP3) in Product Cost Collector

Dear Experts,

I have searched a lot for subjected issue but could not get the clarity. I am pretty clear about PREM (Preliminary Cost) and PPC1 (Standard Cost Estimate). I do not have any clue on Costing Variant Actual (PPP3). Queries are.

1. Use of Costing Variant Actual (PPP3)?

2. Where (in which step/transaction) does any calculation takes place with PPP3 (like PREM calculates value in KKF6N and PPC1 calculates value in CK11N and CK24/CK40N)?

3. Why is it called Costing Variant Actual (PPP3), how it brings value of Material, Activity Price and Overhead cost?

4. Where can we see the difference between PPP3, PREM, PPC1?

Please give clarity on above points. I would be thankful to you guys. Thanks in advance.

Regards

Ruksana