# Ergonomic Recommendations for Range of Control Panel Angle of Touchscreen Kitchen Appliances
## 4 Discussion  
Our study aimed to empirically investigate the ergonomic panel angle range of touch-screen kitchen appliances. Subjective ratings of visibility, physical comfort, and preference were performed while changing the panel angle to achieve this objective. A total of six panel angles (0\({}^{\circ}\), 15\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\)) were considered, and a seven-point Likert scale was used for the subjective ratings of the three measures. Data analyses revealed that the panel angle significantly affected the visibility, physical comfort, and preference ratings. Across all three measures, the mean score distribution showed an inverted U-shape as the panel angle increased. The panel angles of 0\({}^{\circ}\) to 60\({}^{\circ}\) showed scores higher than 4 (\"Neutral\"); in particular, those of 15\({}^{\circ}\) to 45\({}^{\circ}\) showed scores higher than or close to 5 (\"Slightly agree\"). Conversely, in the case of the panel angle of 90\({}^{\circ}\), it showed a low score of close to 2 (\"Disagree\"). Figure 5: Preference ratings with the results of post hoc multiple comparisons. The observed effect of the panel angle on the visibility ratings can be attributed to the difference in angle between the line of sight of the user and the panel according to the changes in the panel angle. Such a difference appeared to determine the task difficulty for the user in checking the power levels displayed on the panel. As the touchscreen panel required the user to state at the panel throughout the operation, visibility was considered one of the most important usability measures. It should be noted that the touchscreen panel served as both a control and a display. According to the existing literature, the best visibility/legibility is guaranteed when the display/panel is perpendicular to the line of sight of the user [2; 4; 6; 50; 51]. According to a guideline for the display tilt angle [47], when the angle (\(\alpha\)) between the line of sight of the user and the display/panel was 90\({}^{\circ}\) (\(\alpha_{optimal}\)), within the range of 70\({}^{\circ}\)-110\({}^{\circ}\) (\(\alpha_{optimal}\)\(\pm\) 20\({}^{\circ}\)), within the range of 60\({}^{\circ}\)-120\({}^{\circ}\) (\(\alpha_{optimal}\)\(\pm\) 30\({}^{\circ}\)), within the range of 50\({}^{\circ}\)-130\({}^{\circ}\) (\(\alpha_{optimal}\)\(\pm\) 40\({}^{\circ}\)), or out of the range of 50\({}^{\circ}\)-130\({}^{\circ}\), the level of visibility was described as \"very good\", \"good\", \"moderate\", \"bad\", or \"very bad\", respectively. Based on the eye heights recorded in the anthropometric reference data for US adults [52], the optimal panel angles that supported perpendicular viewing angles for the 5 th percentile female (142.1 cm) and the 95 th percentile male (175.3 cm) were calculated to be 19\({}^{\circ}\) (\(\alpha_{optimal}\) [5 th %\(\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i} \mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\)] = 90-\tan^{-1}\left[\frac{1421-850}{200}\right]\)) and 12\({}^{\circ}\) (\(\alpha_{optimal}\)[95 th %\(\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i} \mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\mathit{i}\mathit{e}\)] = 90-\(\tan^{-1}\left[\frac{1753-850}{200}\right]\)), respectively. Accordingly, the panel angles that ensured a \"moderate\" level of visibility were determined to be 0\({}^{\circ}\) to 49\({}^{\circ}\) (19\({}^{\circ}\) \(\pm\) 30\({}^{\circ}\)) for the 5 th percentile female and 0\({}^{\circ}\) to 42\({}^{\circ}\) (12\({}^{\circ}\) \(\pm\) 30\({}^{\circ}\)) for the 95 th percentile male, respectively (the case wherein the panel angle was smaller than 0\({}^{\circ}\) was excluded).