Interactive control of graphic output devices.

A software package for the support of graphic output was developed. The main feature is the capability to draw graphs in a Cartesian coordinate system. With up to 60 variable parameters, it is problematic to change them interactively. Classical program languages do not support interaction. Subroutines for various kinds of input had to be written. Most important are other subroutines for reading, writing or erasing datasets at runtime, the name of which need not be known before starting a program. According to the problems, different appropriate methods of dialogue were used: the simple sequential dialoque, command languages and, for more complex input, a syntax analyser. The resulting dialogue is very simple and self-explanatory. The users need not have previous experience with computers; the package was accepted quickly and is now in extensive use.