The G10 command in Mach3 is / can be used to set a fixture coordinate system.
You will find info on the command in the Mach manuals. You need to understand that
there are different "dialects" of Gcode commands and Mach has it's owne dialect for the commands. Read the Mach manual! Linux, Fanuc, Hauss, etc have additional commands
and variations / dialects of the commands, so, again quit getting confused and read / use Mach3 gcode as defined.
What DRO's are you talking about?
Machine coordinates? Part coordinates? Program Coordinates?
See commands G53, G54, G52, G92
You need to understand the different coordinate systems and how they relate to each other. Read the Mach3 Manual.
Roger introduces "his" concept of "space", which is fine.BUT
To get grounded in terminology of CNC Peter Smid's books are an excellent
industry accepted standard.
fwiw,
RICH