questions about FBC in Logix5000

[wendaiyu]

Hi, folks, how’s going?

I have some questions about FBC in Logix5000, plz check attachments:
1, how dose .FD work? I read help manual, but cannot understand it exactly.
2, why values of fault.source and fault.ref. are all 0, but fault.result is 6?

Thanks for your help.