Accounting period options

Hi ,

When i created the new accounting period - system creates the ACC periods with the following period code options like

Opening
. Normal, and
. Closing
and Status are Closed ,Open , stopped .
I think system creates two additional entries like Opening and Closing .
Could you share the logic behind and what is the use these many options ?

Finance I manual - Chapter 2 states:

Microsoft Dynamics AX 2009 always creates two additional periods:

· An opening period to which to transfer the opening transactions from the year-end closing routine. The opening transactions result from the previous years’ balance accounts.

· A closing period to which to enter year-end close specific transactions.