I don't use NC Corrector, but I am interested in your thought process in a quest to learn more.
Are you using a controller that only works with inches and you have a .nc file that was created by someone else, using mm,
and you wish to convert it for your machine?
If it's your own content that you are posting to an .nc file, In F360, you can have your drawing be in inches or mm.
When you post to create your .nc file, it will flag or allow you to flag the file as mm or inch (IIRC, F360 network is down at the moment)
This should generate the proper G20/G21 (inch/mm) flag in the .nc file, for your controller to properly execute your code.
The G20/21 code must match the coordinate info used after it.
As far as I know, modern controllers don't give a darn if the code is in mm or inches,
as long as it knows, it will run either way.
