Probable syntax-error in multi-monitor-, GUI- and clipboard-context

Question

I'm new to AHK and the following syntax doesn't work:

%Final_x% -= (%width% / 2)

Can you spot my error?

Answer 1

After reading the doc on AHK's somewhat quirky varibale syntax I managed to fix it this way:

Final_x := Final_x - width / 2

Thank you all for your contributions!