Your a star, thank you..
I had mispelt weighbridge (as you can see above weighbridge_ref) and $receipt needed to be enclosed in '' to prevent errors.
It's working now so I'm rather happy.
One other thing this page has is a balance, which is basically the sum of "in" minus the sum of "out" giving a balance. The balance doesn't update until the page is refreshed. Am I best of using window.location.replace to refresh the page or is there another way of doing it?