COC Form for including missing documents - Urgent query

Can some please answer if they have ever used COC Form for sending missing documents and if so can you please let me what to mention for the below mentioned fields in COC application form:-

There are two fields:

7. PBS Reference number (If known) - I guess for this I need to mention the reference number that I've received from UKBA as part of acknowledgement to my application which starts with PB

8. Application reference number (If known) - Then what is the Application reference number. Any idea.

Note:- I have received Acknowledgement from UKBA for the application which I have submitted and that starts with PB. Is that the PBS reference number or Application reference number

Thanks in advance for your help and for your response. Much appreciated