This paper defines a new class of unidirectional errors, named t/u-uni
directional errors, which affect at most t bits confined to at most u
bytes of the code word. Codes that are capable of detecting, Locating
and correcting t/1-unidirectional errors are presented. Lower bounds o
n the number of checkbits required for t/1-unidirectional error detect
ion and location are also presented.