Abstract: An LED/photodetector structure is disclosed positioned to cooperate with a daisy wheel print element of a daisy wheel printer and a light interrupter such that under microprocessor control, a stepping motor will rotate and home the daisy wheel print element, sense the escapement pitch corresponding to that element, sense the font weight or impact force level associated with that print element and then cause the carrier to be translated to the left frame, thereby engaging the light beam interrupter with the left frame and forcing it into the light beam indicating the presence or the carrier at a known spacial position for homing of the carrier position.The data carried by the print element in the form of apertures formed in the hub thereof and are all spacially positioned within one semicircular portion of the print element hub.

Abstract: Alignment mark 5 is printed by printer 30 during the same operation in which bar code 3 is printed. Subsequent alignment is by the optical scanner 32 centering on mark 5. In a specific application a factor relating to the vertical position of scanner 32 to printer 30 is obtained by scanning mark 5 shortly after it is printed. This factor is used to position the scanner 32 to read for errors after a line of code 3 is printed.