The man-machine interface at any terminal in a computer system is a likely source of error and can be regarded as a noisy channel. Certain data, such as ID numbers, can be precoded to protect against most-likely errors, including transposition of adjacent symbols and substitutions, as well as deletions and insertions. This paper first considers certain basic requirements for error detection with minimum redundancy. An efficient special coding scheme designed for decimal terminals is described next. Finally, certain cyclic codes are shown to be adaptable to transposition error control when appropriate decoding schemes are implemented.