Where does the Default Salesperson under the commission tab in Sales Order generate from?

But how is the Commission Amt calculated? 
 

Even nothing is getting displayed in the Calculate Commissions Form as below:
 

Thanks in advance.

@jechang The detail lines of the sale order have flag for commissionable that the will determine the commissionable amount the the commissions tab 

Hi, Can we configure as Default Commissionable True in Sales Order screen

I found the solution, if we select ‘Subject to Commission’ check box true in Stock item screen, Sales Order screen Commissionable checkbox will be checked when we create an order with this Item.

Thank you for sharing your solution with the community @shyamalav71 !

How do you specify multiple salespersons as default?

While Creating New Sales order, Sales person id on Item Line  and Default Sales person is not getting Populated to the Sale Order , This Issues Started after the upgrade were all setting for Sales Person and Assignment to Customer remains same . What I am Missing here ?