The main goal of this paper is the evaluation of an assistance system providing a user with on-the-fly Augmented Reality (AR)-based instructions on a Head- Mounted-Display (HMD). In two user studies we address questions concerning the handling with the hardware as well as the interaction with the system prototype.

In a first dual-task study 22 participants executed a manual task while pictures were shown through a monocular HMD and a binocular HMD successively. In a second study 27 participants had to perform on two different assembly tasks either by AR-based assistance, paper manual or video instruction. By observations, questionnaires and structured interviews we assessed the following questions. How intuitive is the control of the HMD hardware, how does the user experience the combination of real task environment and superimposed information, how successful and satisfactory performs the AR-based support compared to traditional types of instruction, what advantages as well as which problems does the concept provide, and which tasks are especially suitable for AR-based instructions.

The results showed that participants preferred the monocular HMD compared to the binocular HMD because of better adjustment and higher comfort. The AR-based assistance during assembly tasks was effective, efficient, and satisfying compared to the other methods. It was experienced as helpful and motivating, but also as less controllable.

233We discuss the usage of monocular versus binocular HMD in different industrial contexts, recommend real-time instructions for tasks with high complexity, and propose gestural user interfaces in order to enable navigation.