The thesis investigates the elaboration of text to improve the acquisition of computing skill by casual users. Manuals are currently the main method by which these users are helped to acquire such skills. However, since there is no control over the way that the manual will be made use of, and no control over the sequencing of task learning, manuals are rarely entirely satisfactory in supporting learning processes. The issue investigated in the present thesis is whether manuals can be modified by the elaboration of text in order to support learning. The thesis also investigates skill measurement techniques, methods of specifying training devices and the applicability of controlled laboratory experiments to this applied setting. A comparison of computing skill measurement techniques showed that the most valid and practical method consisted of short tasks to be carried out using the computing system. These tasks were used as the basis for the study of the effectiveness of manuals. Examination of the pertinent literature in the light of the problems of producing texts for casual users and a model of skill acquisition based on hierarchical task analysis produced several theoretical devices for improving manuals. A formal method of applying the devices to a standard text enabled the controlled examination of the theories…