Where # is one of 96,100,120,144, 150,160,180,200, 225,240,288,300, 360,400,450,480, 600,720,800,900, 1200,1440,1800, 2400,2600,7200
This setting is local to the current print environment and is defaulted and restored when calling a macro.
I have seen several instances where executing a macro that has not been defined (e.g. esc&f30000Yesc&f2X) results in the Unit of Measure being reset the default setting for the printer. Apparently, there is a small bug in the PCL interpreter in some printers (6P, 4000) that causes the restoration of the setting to not occur when the macro is not found.