Calculation of Suggest Item charge assignment on amount

Hi all,

I want to know how Navision calculating values while booking freight entry for purchase invoice through Item charge Assignment and i am using below steps :-

Navison Main Menu>>Purchase>>Invoices : then created new freight document with qty 1 & amt 9000.

then click on Line button>>Item charge Assignment>>Functions>>Get Receipt Lines : Selected BOE no then again click on function >> Suggest Item Charge Assignment >> Amount >> OK.

I checked code unit 5805 & form 5808 functions like UpdateQty and UpdateQtyAsgnt but not getting how system calculating and dividing values & qty for "Qty to Assign" and "Amount to Assign"

So kindly share with me calculation formulas for the same i will be very thankful to you.....

Neel