How to handle complex test results?
Instead of "... save the differences in an Excel table ...", you might want to consider saving these data in an external database (MS SQL, MySql, Oracle, some PDO compliant database, etc).

And then use the Forena module to build custom queries to retrieve the data (directly from such database) and create custom reports from them. Those reports can then be exported in PDF or Excel. For that you just have to enable the desired Forena report options called "document format".

Refer to my answer to "How to download Database results as PDF or in EXCEL" for more details.