Several systems have been developed to produce the complete inventory of IPA symbols in computer-coded form. Each has its own detail of coding, with a common core (albeit fairly small) of phonetically or graphemically logical key and ASCII assignments that can be identified across systems. Variation in the assignment of symbols to codes and keystroke locations is the result of different configurations of input device and of output device, and of differences in local convention and ease of character entry, of immediate needs in the transcription task, and of project objectives. The two major categories of coding objectives are: (a) for the purpose of identifying individual graphic IPA symbols by number, and (b) for the purpose of specifying the phonetic properties of the sound represented by each symbol or combination of symbols for the efficient encoding, recall, and manipulation of that information in a computerized data base.