How would I find the locations where persistent variables 500-600 are stored on my hard drive? If possible, I'd like to write to these variables with the software I use to generate and edit my gcode, so their values can be found and used in my macros.

They are stored in the XML file.  Make a note that anything you update in the current session is not saved until Mach3 closes.  BUT you can force a save if needed.

(;-) TP

Thanks as ever!

M21