Opening Period and Foreign Currency

Hi Sirs,

Could you answer me questions as below ?

Q1) What is mean by opening period ? For example, if we execute MRP Run, we have options to select "Creste PR" or "Creation PR in opening period". Do you know what is the opening period ?

Q2) In the following two situations, could you advise whether current exchange rate can be used in invoice verification ?

1 - Exchange rate is specified in PO.

2 - Invoice is created without reference to PO.

Also, is it possible to use current exchange rate in goods receive ?

Tks,

KH Fong