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How to add totals at the bottom of “Purchase order lines” section or “Invoice Journal” section:
1. Go into any purchase order
2. In “Lines”, go down to Purchase order lines:
3. Right-click at “Net Amount” column, move cursor down to “View column totals" and select “Sum”:
4. It will automatically put the total at the bottom of the lines and it will save this function for all of the POs you view:
5. You can do this for “Invoice Total” too: At top ribbon, click on “Invoice” and then go to Journals and then “Invoice”:
6. Right-click on “Invoice amount” then “View column totals”, then “sum” (like above):
It
adds
the
Sum total
at
the
bottom
of
your
screen:
8. 
This is especially helpful when you are working in a blanket order (unit price is $1.00): the difference between the “Net amount” and the “Deliver remainder” should equal the total “Invoice amount”: $5,500 – $1,671.95 = $3,828.05