A study examined how well existing audience theory fits what really happens when writers write on the job. This ethnographic study focused on the process of revising one chapter from a guide to the DOS computer operating system designed for use by novices as well as intermediate and skilled users. Preliminary findings confirmed much of audience theory, but with some qualifications. Preliminary findings indicated that, as audience theory predicted, the publisher classified its readers by skill and by professional background and that the audience for this chapter included people within the company. Implications of this study are that audience constraints on the job are more complicated than technical writing textbooks admit, and that, in industry, editors of computer documentation need more immediate and more salient information about their external audiences. (Two figures are included.) (RS)