I am new to CNC and Mach3. I have a 3 axis engraving machine.  I was able to set up my machine without any problems. I used generated a .dxf and g-code with 2L. I was able to execute it and all looked great and it executed in inches (yesterday). I reloaded the g-code and today it executes the same values but in mm's. Really tiny, i.e., the 2" square is now 2mm's.  I am sure it is something really simple. I know its not the native units under configuration. I checked that.  Thanks in advance for any help.

ADD a G20 to the start of the Gcode or issue a G20 from teh MDI line before you start the program.

You need to SET the G20 mode so MACH3 runs in INCHES. G21 set it to run in MMs.

Look at teh top right of the main screen, the modal line , it shows what modes are active.

Just a thought, (;-) TP

Thanks,  Just added the g-code  "G20" as first line and it worked