how to get BELNR from MR21 transaction.

Hi,

I am currently working on one enhancement.

For MR21. when any price change has been entered for the period and the valuation area. after updation

when i click the Display Document tab. it is calling the Transaction CKMPCD. with BELNR (Document Number ) and KJAHR (year). i am not able to find how it is fetched.

can any one tell me how to fetch the BELNR and KJAHR for the documents posted.

THanks In Advance

Guhapriyan Subrahmanyam