I have a Point of Sale system that I made. I have a quantity field for the inventory items. It is a calulation of QTYsold and ShelfCount.
QtySold is a summary field of all the times that item sold and count is an editable field that is the count of shelf items. It continues to get added to the more we sell an item.
Example: We have 9 pcs in stock, and sell them all. Count is at 9, QTY sold is at -9, QTY on hand field now shows 0.
We get in 5 pcs count is now 14, QTY SOld is at -9, QTY on hand field now shows 5.
Any better ideas? This one seems crappy.