If you decrease the item quantity, the GL Source Account you enter here is debited, and the item's inventory account will be credited. If you increase the item quantity, the GL Source Account you enter here is credited, and the item's inventory account will be debited.
To display a list of existing accounts, type ? in this field, or select the Lookup button. To add a new account, type + or double-click the field, which displays the Maintain Chart of Accounts window.