Hmmm. It looks like I can't solve this by myself.

There is C++ code which I can probably use part of it to give me what I need. Except. I don't know C++ so I can't convert C++ to VBA. (I've tried but it isn't easy converting from one language to another. Particularly when you don't know the original language!)
And there are no bilingual (C++ & VBA) programmers on ExcelForum (or if there are - they are in hiding!)

There are various Python scripts out there (which I found by googling) that I MAY be able to use part of their code to get the variable I'm seeking.
Except (you guessed it) I don't know Python. So I can't convert Python to VBA (I've tried but etc. - same problem as converting C++ to VBA).

I don't suppose there are any Python/VBA programmers on ExcelForum? (Although the C++ code looks far more promising)