Finding external formula links in Excel

I work with a lot of Excel spreadsheets. I mark using Excel, because Excel adds up so beautifully, using tick boxes to mark things present - or to indicate that those things are not present. The result is a map of what has been done, what has not been done: and what grade that results in. And I have found I get a more objective mark because of those tickboxes: I might think a student has turned in…