Purchase Order Headers and VAT

A few basic questions for you all:

1.  When you create a purchase order in 12.1.3 is the header amount that is shown always net of VAT (does not include VAT).

2.  When you set up a signing limit in Purchasing does it look at the purchase order total amount as on the header or does it look at the VAT inclusive amount.

3.  Should the Purchase Order Print always show the net amount (does not include vat)

4.  Where are the settings for purchase order vat if these indeed exist.