I'm not sure what you are trying to do. In your template, the current node is a Product element. You product element does not have an attribute called Number or Value, so the expressions @Number and @Value will select nothing. And I'm not sure whether you really intended to compare these values with all the product numbers in the whole document, which is what "= /Products/Product/Number" means.
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference