1 This International Standard specifies a set of check character systems capable of protecting strings against errors which occur when people copy or type data. The strings may be of fixed or variable length and may have character sets which are a) numeric (10 digits: 0 to 9); b) alphabetic (26 letters: A to Z); and c) alphanumeric (letters and digits). Embedded spaces and special characters are ignored. 2 This International Standard specifies confor-mance requirements for products described as gener-ating check characters or checking strings using the systems given in this International Standard. 3 These check character systems can detect: a) all single substitution errors (the substitution of a single character for another, for example "4234" for "1234)"; b) all or nearly all single (local) transposition errors (the transposition of two single characters, either adjacent or with one character between them, for example "12354" or "12543" for "12345"); c) all or nearly all circular shift errors (circular shifts of the whole string to the left or right); d) a high proportion of double substitution er-rors (two separate single substitution errors in the same string, for example "7234587" for "1234567)"; and e) a high proportion of all other errors. 4 This International Standard excludes systems designed specifically to: a) permit both error detection and automatic correc-tion; b) detect deliberate falsification; and c) check strings interchanged solely between ma-chines. 5 This International Standard is for use in infor-mation interchange between organizations. It is also strongly recommended for use in internal information systems.