To change the quantity of a product registered on a sale at checkout:
Click on the productin question, use +/- to adjust the quantity.*
Negative quantity is used for returns.
Tip: Next to the search field at checkout, you can adjust the quantity before the product is scanned or selected. For example, you can click on the quantity field, select 3 and then scan a barcode or click a quick button. 3 of the same product will be added. The quantity selection automatically returns to 1 (default) when an item is selected.