direct unit cost excl./incl. vat changing in purchase line

Good day, I'm a newbie developer in MSNAV, I have a problem passing a value from my customized (amount) table to purchase line (direct unit cost excl./incl. vat). My question is, what exactly is the real column name of direct unit cost excl./incl. vat in purchase line table? I tried passing my value to Direct Unit Cost but its not showing or where can I find the codes that triggers the column changing of the said column in purchase line? Please help me thank you in advance..