Actually, my approach would be different... for memo field, it is quite difficult to get good statistic results, like input/output count of every inventory...

My approach is
1. A table to register every sale items
2. A table to register every receipt printed

e.g.
table_item

ID_log        AUTO_INC  PRIMARY
sale_receipt  NUM(8,0)
sale_datetime DateTime
sale_person   CHR(5)
item_ID       CHR(9)
item_QTY      NUM(6,0)
item_PRICE    NUM(9,2)
... and so on

Table_receipt

ID_log         AUTO_INC
sale_receipt   NUM(8,0)
sale_item      Memo
sale_total     Memo
sale_paid      Memo

The receipt is stored in this way:

cSale_item=''
SELECT * FROM table_item WHERE sale_receipt = nReceipt INTO CURSOR cTmp
SELECT cTmp
GO TOP
FOR x = 1 TO RECCOUNT('cTmp')
   cSale_item= IIF(!EMPTY(cSale_item),cSale_item + CHR(13),'')+ ;
   PADR(alltrim(item_ID)+ 'x'+ alltrim(str(item_qty)),29,'.')+' $'+str(item_price,9,2)
   SKIP IN cTmp
ENDFOR
USE IN cTmp

&&... You can prepare sale_total & sale_paid in this way

INSERT INTO table_receipt (sale_receipt,sale_item...) values (nSale_receipt,cSale_item...)

After that, you can preview the receipt by its sale_receipt in Preview windows; which in fact, more convenient to export to PDF file for record keeping.