Can you set up in the field definition "Amount Sold" Field (assuming a field of type number) a validation by calculation, to be
=/> than the Inventory on Hand field?
Set the alert message to warn the user to change the entry in the Amount Sold field.
Since I'm not Guy Stevens (who has provided some good assistance here in the forum), I don't know exactly how you set up your inventory management system to calculate quantities on hand. There is more than one way to do this. Do you have a field in a related products table that stores or calculates the quantity on hand for that product? or perhaps some other related table if you need to refer to quantity on hand in the context of a particular location?