https://docs.google.com/spreadsheets...it?usp=sharing
This is what I use, when using old school tools like a ruler to mm. I try to measure to the nearest 1/4 mm, which could create some inaccuracy, but I typically find changing one or both by 1/4 or 1/2 mm doesn't make a big difference.
I'd love some kind of app that could detect size and centering, but until then, this has been very helpful to me. It has kept me from submitting certain cards or helped me decide whether to check "no qualifiers" when submitting.
Hope the link works