## 4 Discussion  
The order of the assembly/disassembly and types of job instructions were randomly arranged for each participant. It was, therefore, reasonable to assume that learning effects contributed equally to both the task and type of job instruction in this study. The time to complete the task was adopted as the main variable to indicate the performance of the participants. For inexperienced participants, assembly tasks required significantly (_p_ < 0.05) longer time to complete than disassembly. This was not surprising at all. Disassembly is always easier and less time consuming than assembly. Our data showed that disassembling the four components needed only 60% of the time of assembling them. Gender was also a significant (_p_ < 0.05) factor affecting the time to complete the assembly/disassembly tasks. Males could complete their tasks faster than their female counterparts. The time to complete the tasks for male participants was only 90% of their female counterparts. This gender difference might be attributed to the motor skills of males and females to tighten and loosen the screws. For job instructions, the participants using AR displays spent significantly (_p_ < 0.05) longer time than those of the video display and printed manual conditions. Using AR display, on average, spent 118 and 87 s longer than those video display and printed manual, respectively, in performing the assembly and disassembly tasks. This was consistent with the findings in the literature [32,33] that wearing an AR device might not lead to better efficiency than those who did not wear one and watched a wall-mounted monitor instead. This, however, was inconsistent with the findings of some of the other literature [16,30,31]. All the participants were familiar with clicking a mouse to activate a continue button on a laptop display and to flip a sheet of paper of the manual. On the contrary, none of them were familiar with tapping on the \"next page\" button on the virtual-displayed instruction on the HoloLens 2. This might result in a longer time accessing the job instructions. The virtual hand(s) to highlight the push/pull movements was one of the innovations of the job instruction we created using the Dynamic 365 app in HoloLens 2 for the tasks. They clearly indicated what the participants should do using their hand(s). However, the participants might be distracted by this innovation and responded slower because of the attraction of the hand(s). In addition to the time to complete the task, the errors made by the participant was also an important variable to assess the performance of the tasks. There were no errors made in the disassembly tasks. There were, however, 28, 13, and 7 errors in the printed manual, video display, and AR display conditions for the assembly task. The majority of the errors were observed when the participant was assembling the power supply. This component has three cables. Two of them needed to be plugged into two slots on the motherboard and the third needed to be plugged into the DVD drive. Most of the errors were that the participant simply put the connector into the slot without pressing it firmly. An assembly task failed so long as any cable connector was not well connected. The numbers of unsuccessful assembly for the printed manual, video display, and AR display conditions were 14, 8, and 5, respectively, out of 21. Job instruction via AR display apparently led to less failed assembly, which implies better quality of the tasks. This advantage might be attributed to innovation of virtual hand(s) to highlight the hand movements to be performed. Our results in the errors associated with the AR device were consistent with the findings of [PERSON] et al. [29]. The hand dexterity of the participants was measured using both the PPT and MDT. The PPTd was negative correlated with the time to complete the assembly task for both video (\(-0.47\), \(p<0.05\)) and AR instructions (\(-0.52\), \(p<0.05\)). This was reasonable because high PPT number implies high hand dexterity.