Pictured in Figure 3.11.10-20 is an example of Form 3753, Manual Refund Posting Voucher, overlaid with a portion of the Form 813, Document Register. An arrow with a bubble box (stating, Primary Transaction Code 840 must match Form 813 Header) contains (two) arrows pointing to 840 on the Form 3753 and the Form 813, respectively. 840 is in the Primary box (Transaction Code, Box a), located on the Form 3753 and is contained in the Trans. Code box, located on the Form 813.