# Comparing Augmented Reality-Assisted Assembly Functions--A Case Study on Dougong Structure
## 5 User Study
### Analysis of Experimental Data  
The experimental data were analyzed with both objective and subjective measures. The former evaluated the experimental process using the video clip recorded. The quantitative results included the time spent and errors committed by the subjects in each assembly step. The two assisted systems and paper-based instructions contain different assembly steps, described as follows:  
* Part recognition: the user identifies the part with the information provided in different media. The time spent in this step is estimated from the end of the previous step to the moment that the user's eyesight left the information.
* Part fetching: the user selects, grasps, and moves the part from the storage area to the work area.
* Part confirmation: only the AR-based system has this step, where the system confirms that the part taken by the user is the correct one.
* Assembly confirmation: only the AR-based system has this step, where the system confirms that the current assembly step is properly completed.
* Task recognition: the user comprehends the assembly process. The time is measured from the time when the user takes the part to when the assembly starts.
* Assembly: the time is measured from when the user starts to assemble to the moment that the \"Next\" button is clicked.  
This study differs from previous studies in that not only the time spent by the part identification and assembly steps was explored, but also the time consumed by the user to comprehend the assembly instructions. It was observed that after the participant had chosen the correct part, they still had to read the instructions in order to assemble the part in the correct position and orientation. Most subjects seemed unfamiliar with the Dougong assembly despite the demonstration given to them. The time spent in understanding the instructive information revealed a subject's cognitive processing time (before the actual assembly). It also helped evaluate the efficiency and effectiveness of the assisted functions provided.  
[PERSON] et al. [7] classified the errors of the manual assembly into the part orientation and position errors. In this study, two additional error types are proposed based on the observation  
Figure 11: (**a**) Experimental environment and (**b**) a typical AR-assisted experiment session.  
during the Dougong assembly: part fetching error and incomplete assembly. The former refers to the situation in which the user fetches a wrong part. This error may occur owing to the user's incorrect recognition of the part to be assembled, or mistakenly fetching a wrong one from the part storage. Incomplete  assembly indicates that the assembly task is not properly accomplished with the parts not aligned precisely or their relative position not achieved.  
As mentioned previously, a post-experiment assessment using the NASA-TLX questionnaire [9] was conducted to subjectively evaluate the workload while using the systems. The subjects were interviewed and their feedbacks regarding the experiment were collected. A one-way analysis of variance (one-way ANOVA) was applied to analyze the following factors: the time of each assembly step, the assembly errors, and the questionnaire score for the paper-based instructions and the two AR systems. If a statistically significant difference exists in the ANOVA, [PERSON]'s method [21] is then used for detailed comparisons. It compares all possible simple and complex pairs of means with a narrower confidence interval.