Such calculation is opening on documents with the type of purchase Import, where the subject is not identified for VAT purpose in one of the member states of the Community, which you determine by prefix of the tax number (see Basic data of the subject). 

If the VAT prefix exists and is a prefix of one of the member states of the Community, the calculation for gaining of goods from the Community is displayed (see Gaining of goods from the Community).

In such case the invoice is issued in a foreign currency. For posting into balance accounts/general ledger use the middle rate of Bank of Slovenia. In tax records you have to display the tax basis, which is calculated with the use of the customs rate as entered on the SAD. So:

SAD

It is the case for the described data about SAD for the import of goods: that they are mentioned for INPUT of data about the linked SAD for import; that is about the data that is displayed in the Special record on input VAT at the import of goods.
Document type	document type of SAD for import. By default this is EU0.
Document	number of SAD document for import.
SAD	number of SAD is made of three parts, the data can be found in the chapter A SAD for import (for detailed presentation see Use of data from SAD for import in tax records): check-list number consecutive SAD number from the check-list )(chapter 5 - Special records) date of SAD (chapter 5 Special records)
Customs procedure	the code of the requested customs procedure from the SAD for import (chapter 4 - special records). For ordinary import of goods the code "40 - release of goods into duty and tax free goods movement."