I have a table where I enter INVENTORY PARTS. The table allows me to add a record for the parts that come in and add a record as the parts are used. Since pricing changes for the parts, I have a master table called PART LIST that houses the complete list of my parts. This PART LIST has a relationship to the INVENTORY PARTS where it summarizes the average cost for all the parts in the inventory. When I use a part, it cost it according to this average price. How do I lock that average price when I save a record? Right now, my historical cost data changes based on the average price....Once I "expense" or "use" items from the inventory at the Average cost, I need that historical data to not change.