Question regarding Balance of Payment

Hi guys,

My conceptual understanding on Balance of Payment (BOP) is weak and I have a hard time trying to tie the concept to real life application.

Can someone please explain how Official Reserve play into all of BOP equation? If Current Account is positive and Financial Account is 0, then Official Reserve have to be negative, does this mean Official Reserve increases by the amount current account has.

The Curriculum mentioned that Official Reserve rarely change? why is that?

Practically speaking:

current ac + capital ac + financial ac = 0 … financial a/c includes official reserves

CFAI in their analysis assumes that:

current ac + capital ac = 0 … financial ac is included in capital ac

Please correct me if I am wrong