[Form]![SupplyData-Input]![CustomerControlNumber]
you would use the forms! syntax to make it easier to use.
YOU are doing this by opening the query directly, and requesting the data in an input box. The customernumber may be a "non-obvious" account number, which you are forcing the user to know- how does he find this?
instead, if you have a form (in this case - SupplyData-Input)
with a field called CustomerControlNumber
and no doubt a commandbutton called "Go" or something similar.
The go button calls code to open the query. Instead of prompting you for a code you may not know, the query gets the customercode by using the controlnumber field on the form.
Now the controlnumber on the form may actually be a combo-box, not just a numeric or text - which allows the user to pick a customer by the name he knows, but which then uses the underlying controlnumber to drive the query
see - easier, not harder.