Codabar was developed in 1972 by Pitney Bowes, Inc. It is a discrete, self-checking symbology that may encode 16 different characters, plus an additional four start/stop characters. This symbology is used by U.S. blood banks, photo labs, and on FedEx airbills. Since Codabar is self-checking, there is no established checksum digit. This symbology starts and finishes with one of four possible characters A, B, C, or D.