## 7 Discussion on User Studies and Suggestions for User-Centric Task Assistance
### Discussion on User Studies  
#### 7.1.1 Evaluation for the Visual Context  
For the 3D matching task concerning the visual context in the first user study of Section 4, the stereo rendering and direct augmentation method took approximately twice as long to complete the task compared to the non-stereo rendering and indirect augmentation. The reason for this is that the non-stereo rendering and indirect augmentation can provide more information than the stereo rendering and direct augmentation due to the broader FOV through the camera than through the optical display. Due to this limitation, in the stereo rendering and direct augmentation, the user had to move their head frequently to check the location of the target object to select, translate, and rotate the virtual control object.  
In the second user study in Section 5, the stereo rendering and direct augmentation with a wider FOV (but still similar or narrower than a camera) showed the best task performance. In this experimental evaluation, the stereo rendering and direct augmentation with a larger FOV made it possible for the user to recognize the position and orientation of the target object easily, and the matching task with the control object was more effectively performed. In particular, if the FOV of the stereo rendering and direct augmentation and that of the non-stereo rendering and indirect augmentation were similar, the stereo rendering and direct augmentation was more effective than the non-stereo rendering and indirect augmentation due to the visual matching between virtual and physical artifacts. On the other hand, the non-stereo rendering and indirect augmentation allowed the physical objects to be visually overlapped only through the display of the smart glasses. Thus, the video image was mismatched with physical objects, confusing the user while they performed their tasks.  
Depending on the role of the control and target objects for the 3D matching task in the first and second experiments, there was a difference in task performance. The reason for this result is related to whether the control object with which the user interacts is virtual or real. For the 3D matching in the first user study, the control object was virtual. Thus, when the user moved and rotated the control object, the control object always had to be in the user's field of view. However, as the control object in the second evaluation was real, it was not necessary to place the control object in the user's field  
Figure 24: Evaluation result based on NASA-TLX of the real use case.  
of view in the AR smart glasses. That is, when the user recognized the location and orientation of the target object while holding the control object, the task could be conducted without looking at the control object.  
According to the qualitative analysis and the interview for the visual context-based methods, the stereo rendering and direct augmentation method provides a promising direction for wearable AR as it can support almost exact matching between the virtual and physical objects in wearable AR. However, some participants mentioned that the stereo rendering and direct augmentation also had a limitation in providing enough information due to the narrow FOV, which prevented them from performing the given tasks naturally. In the non-stereo rendering and indirect augmentation with the video background, physical objects were duplicated through the display of the smart glasses. Interestingly, some users performed tasks just by looking only at the display of the smart glasses in the video-based augmentation. On the other hand, the non-stereo rendering and indirect augmentation without background was not suitable for the task assistance as there was much difference between the virtual object and the real environment. We also found similar results from industrial workers in a real industrial environment. Therefore, the analysis and evaluation results will be effectively utilized in designing and implementing manufacturing services using AR smart glasses.