# Ergonomic Panel Angles for Kitchen Appliances with Cooker Knobs
## 4 Discussion
This action, combined with the panel height set at 850 mm, caused the elbow and shoulder to lift, resulting in an uncomfortable posture (Figure 6a). Conversely, during clockwise rotation of the knob, forearm supination occurred, increasing the degree of wrist extension and leading to awkward and uncomfortable postures (Figure 6b). In this experiment, when the panel angle was 0\({}^{\circ}\), the maximum wrist extension induced while operating the knob averaged around 45\({}^{\circ}\), occurring during forearm supination. For the shortest participant, who was 155 cm tall, the maximum wrist extension exceeded 60\({}^{\circ}\) due to the panel height of 850 mm. The angles of wrist extension, accompanied by elbow/shoulder elevation and forearm supination, were greatest at a panel angle of 0\({}^{\circ}\) and decreased as the panel angle increased. On the other hand, when the panel angle was steep, such as at 90\({}^{\circ}\), the combination of forearm pronation and wrist extension led to an increase in wrist extension, resulting in uncomfortable movements. In this experiment, when the panel angle was 90\({}^{\circ}\), the maximum wrist extension averaged around 57\({}^{\circ}\), which occurred during forearm pronation. The degree of wrist extension, accompanied by forearm pronation, was greatest at the panel angle of 90\({}^{\circ}\) and decreased as the panel angle became less steep. Considering that the wrist extension range of motion (ROM) for the 5 th percentile of US adults is approximately 41\({}^{\circ}\)[42], it is likely that users with limited ROM may experience discomfort when the panel angle is either very shallow, such as 0\({}^{\circ}\), or very steep, such as 90\({}^{\circ}\). Therefore, taking into account wrist extension accompanied by elbow/shoulder elevation and forearm supination/pronation, a panel angle around 45\({}^{\circ}\) (ranging from 30 to 60\({}^{\circ}\)) is recommended to avoid discomfort. This range aligns closely with the findings from our experiment, where panel angles between 30 to 90\({}^{\circ}\) yielded physical comfort scores above 4 (\"Neutral\"), and those between 45 to 60\({}^{\circ}\) produced scores nearing 6 (\"Agree\"). The impact of panel angle on user preference can largely be attributed to both visibility and physical comfort. As previously discussed, the user's viewing angle and posture while interacting with the control panel shifted as the panel angle changed from 0 to 90\({}^{\circ}\). It is believed that these variations in visibility and physical comfort likely contributed to the user's preference. The pattern of mean preference scores closely mirrored those of visibility and physical comfort (Figures 3-5), with panel angles between 30 and 90\({}^{\circ}\) yielding scores  
Figure 6: Knob operation posture at a panel angle of 0\({}^{\circ}\). (**a**) Forearm pronation; (**b**) Forearm supination. above or near 4 (\"Neutral\"), and angles between 45 and 60\({}^{\circ}\) scoring higher than 5 (\"Slightly agree\"). These results suggest that both visibility and physical comfort directly influenced user preferences. In fact, significant positive correlations were found between preference and visibility (r = 0.78, \(p<\) 0.001), as well as between preference and physical comfort (r = 0.85, \(p<\) 0.001). One interesting result from the additional analysis of this study was that the variation in preference scores for different panel angles differed in accordance with the user's height. A box plot showing the standard deviation of preference scores for six panel angles by user height group is provided in Figure 7. It was revealed that users in the shorter group (165 cm or less) and the taller group (180 cm or more) exhibited relatively large variations in preference scores across the panel angles (SD = 1.96 and 2.06, respectively). In contrast, the medium-height group (165-180 cm) showed a relatively smaller variation in preference scores (SD = 1.50).