Converts a value in millimeters to the unit set in the system settings (millimeters or inches).
mm_to_setunit(value)
Convert 25.4 mm to system units
mm_to_setunit(25.4); // returns 1 if settings are in inches, 25.4 if in mm
Convert 100 mm to system units
mm_to_setunit(100); // returns 3.937 if settings are in inches, 100 if in mm