## 3 Materials and Methods: Eye-Tracking Experiment
### Data Analysis and Result
#### 3.5.3 Areas of Interest Analysis  
In eye-tracking experiments, defining areas of interest (AOIS) is the best way to test how long and how many times subjects pay attention to a product. By dividing the experimental materials into multiple areas of interest, the corresponding eye-tracking data can be obtained and analyzed through eye-tracking experiments [18], which can reflect the users' tendency to observe the product with interest.  
In this study, the user's area of interest (AOI) in the eye-tracking experiment consists of the logo, console, and observation window, etc. Additionally, the experiment is carried out in combination with the data on the user's first fixation time and total fixation duration. The time to the first fixation is the amount of time the user spends observing the element, from the time when the image is displayed to the time when it is noticed by the user. The shorter the time is, the more attractive the element is to the user [37]. The total fixation duration is the total time that user spends in an area, with longer fixation durations reflecting higher levels of interest in what the user are looking at [38]. Table 2 offers an illustration of the machine tool picture AOI.  
To reduce data deviation caused by the observation of the machine tool pictures due to uncertain factors, it is necessary to analyze the AOI data by combining multiple machine tool coating experimental materials of the machine tools. Table 3 shows the AOI data list of the coating interface of the machine tools.  
The shorter the average time to the first fixation is, the less time it takes for the subjects to notice the area of interest. This indicates that the area is more likely to attract attention. Otherwise, it is less likely to attract attention. The shorter the average total fixation  
\begin{table}
\begin{tabular}{c c c c} \hline
**AOI of a Single Machine** & **AOI of Multiple Machine** & **AOI List** \\
**Tool Picture** & **Tool Pictures** & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Illustration of the machine tool picture AOI.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Elements of Concern**} & **LOGO** & **Machine Tool Model** & **Machine Tool Bed** & **Observation Window** & **Base** \\ \hline Time to First & frequency & 10 & 9 & 27 & 30 & 8 \\ Fixation (s) & average & 1.37 & 2 & 2.14 & 0.36 & 3.7 \\  & total & 13.73 & 18.04 & 57.76 & 10.92 & 29.63 \\ \hline Total Fixation & frequency & 10 & 9 & 27 & 30 & 8 \\ Duration (s) & average & 0.55 & 0.56 & 0.8 & 1.44 & 0.48 \\  & total & 5.52 & 5.05 & 21.63 & 43.14 & 3.82 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The data on the machine tool AOIs.  
duration is, the less total time it takes for subjects to observe the area completely, which means that the information conveyed in this area is relatively simple or less attractive to the subjects. Conversely, the longer the average total fixation duration is, the more complex the information conveyed in the area is, and the more attractive it is to the subjects.  
From the data calculated in the above table, it can be concluded that, among the relevant elements of the coating design, the subject's average first fixation time, with respect to the observation window, is 0.36s at the shortest, while the average total fixation time is 1.44s at the longest. This indicates that the design element is the most likely to attract attention. Because of its complexity, the longest time is required for the subjects to observe it, and it is their main area of interest. The machine base has the longest first fixation time and the shortest total fixation duration, being 3.7s and 0.48s, respectively, and it is the weakest area of attention, followed by the logo, the machine tool model, and the machine tool bed. The data provide support for the optimal design of the coating scheme of the machine tool.