Plugging the charger into the HP Woodstock series of vintage calculators will damage the calculator if there are no batteries present or the installed batteries are dead.  This plug provides a reminder that the charger is not to be used.   Printed with TPU/Flex at 0.2 mm layer settings and 15% infill.  For a more transparent plug with clear TPU, add a layer height modifier for the first 5mm to print with 100% infill leaving the rest at 15% so it is not too hard to unplug.