While formats and conventions of scientific and technical writing vary from field to field, the transcendent requirement is precision, so that the work can be understood and, if necessary, reproduced. Science teachers undoubtedly tell students about the importance of precision in collecting data and analyzing results; what is less commonly emphasized is the need for precision in writing. Part of the problem is that students lack experience with the conventions of scientific writing, so exposure and practice is essential. The term papers and essays that they do write presume that readers--graders, usually--have prior knowledge of the subject. Students ordinarily lack experience writing for readers without prior knowledge of a subject, and they must be taught how to provide the context needed to understand their writing. This article presents an exercise that provides a starting point for teaching students to write from a position of expertise. (Contains 1 table and 5 figures.)