An add-on bar code reading apparatus used in a bar code reader identifies a block of a main-part bar code by detecting start and end guard-bars, determines a right end of the main-part bar code based upon whether all the characters in the block carry even parity, detects the add-on bar code...http://www.google.com/patents/US5686715?utm_source=gb-gplus-sharePatent US5686715 - Add-on bar-code reading apparatus in a bar-code reader
