One of the most widely used analysis packages for regional and teleseismic seismic data is SAC (the Seismic Analysis Code). It was developed in the 1980s by nuclear test monitoring agencies in the United States, who freely made the source code and paper documentation available to academic users. From this initial distribution, the analysis package became popular in academic circles due to its ease of use and suitability for research data analysis in seismology and geophysics.

SAC's documentation was on ring-bound paper shipped along with the nine-track half-inch source code tapes that you received in the post. The academics in receipt of them generally made copies from the master document and distributed them to colleagues and students. They also tutored new users on the use of SAC, guiding them through their first session and then left them to the documentation. Consequently, much of the knowledge of SAC was passed tutorially from an experienced user, not unlike trade apprenticeship. Those intrepid enough to find and read the documentation usually exceeded their tutors' ability. The far fewer who delved into the source code learned of undocumented features of great utility. The usual reasons for this puzzling knowledge gap apply: in software development, documentation always lags feature development and, for SAC, new releases were sporadic and focused on new capability.

The original SAC documentation consisted of: (1) tutorial guide; (2) command table; (3) detailed command descriptions; (4) SAC file structure internals; (5) auxiliary program guide for programs to turn graphics to hard-copy form.