## 4 Results of Research on the Accuracy of Marking Objects with Eye-Tracking  
The purpose of conducting research is to build a system that introduces an additional verification step for the correctness of the operator's decision. Figure 2a shows the current state of the system. There is only an X-ray device and an operator who visually searches for prohibited objects in the screened images. In the proposed solution, there is a new element in the system (Figure 2b), a module that collects data on the location of the gaze and the location of the forbidden object (TIP). With these data, it is possible to verify if the operator is actually looking at the prohibited object when the alarm is triggered. A self-built training simulator was used for the study (Figure 3). The simulator features a design that replicates the actual workstation of a safety counter operator. Since dual-view X-ray viewers are very often used at airports and have two 19\({}^{\prime\prime}\) monitors for image evaluation, an analogous arrangement was used in this study. The simulator was additionally equipped with an eye-tracking system mounted as a bar under the monitor screen. A commercially available measurement solution (eye-tracker) operating at 120 Hz and an average delay of <13 ms was used. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**No. ** & \(n_{c}\) & \(n_{ct}\) & \(n_{cf}\) & \(HR\) & \(HR^{\prime}\) & \(\Delta HR\) [\%] \\ \hline
1 & 23  
The research began by checking the device's overall accuracy in different parts of the displayed image. At 170 locations on the screens (selected at random positions from a uniform distribution), points where the eye should be focused were displayed sequentially, one after the other, at fixed intervals. The subject was given 10 s to mark the displayed marker with their eyes. For each measurement, the coordinates of the displayed point on the screen and the coordinates of the gaze focus were recorded. The collected positions indicated the distance measured in pixels from the lower left corner of the screen. Then, for each point, the absolute error \(\Delta l\) was determined for each test person. The error represents the distance between the point displayed and the focus of the subject's gaze. The set of points was drawn once, and each subject observed the points displayed in the same order. For each point, the average error value \(\overline{\Delta l}\) was determined from a sample of 30 people. This brought the total sample to 5100 locations (170 locations \(\times\) 30 participants). Due to the lack of need for knowledge of the screening operator in this study, non-certified individuals participated in the survey. The study included people between 20 and 60 years of age who had different eye conditions (without glasses and lenses, with glasses, with lenses) to take into account the applicability of the system for different groups of people. Average error values \(\overline{\Delta l}\) (the error value is presented by the diameter of the circle) depending on the location on the screens are shown in Figure 4.  
Figure 4: The average values of the errors of the points of gaze focus depend on the place on the screens. Figure 3: We built a replica of the device for the implementation of research. The results obtained (Figure 4) indicate that the error is not a constant value. A different error value was obtained at each of the analyzed points. A certain trend can be seen, which indicates higher error values in the middle part of the screen compared to the lower and upper parts of the screen. However, these values are not important enough to make separate calculations for different areas of the screens. The minimum value of the average error \(\overline{\Delta}l\) is 40.7 px. The maximum value of the average error \(\overline{\Delta}l\) is 105.7 px. The dispersion between these values is 65 px. Figure 5 shows a summary of the maximum, average and minimum values of the error with respect to the size of the example forbidden object.