how to measure 51% whiteness in breed standard

Thank you for the detailed response to my question, where you described why the color standard exists. Back to my original question, though, I am curious how the percentage of whiteness is measured on a dog. For example, how would one differentiate a dog that is 51% white from one that is 50% white?

It may be tough to do when it gets that close to the cut-off, but my puppy seems to be awfully close to the cut-off and I'd like to know whether or not she meets the standard.