1. Search for and bring up the Product Details screen for the stock item or labour/job code that you want to stop updating the quantity of. If you are unsure on how to search for a product then please use the guide titled; How to Search for a Product.
2. Click on the button underneath Don't Upd. Qty to change it from the default NO to YES.
3. Once you have selected YES clear the Qty On Hand field so that it is blank and click on the green 'Save' button down the bottom right of the screen.
Now when you enter this stock item or labour/job code onto an invoice the Qty On Hand field will stay blank, it will no longer go into a negative.