# Ergonomic Panel Angles for Kitchen Appliances with Cooker Knobs
## 4 Discussion  
This study aimed to empirically determine the ergonomic knob panel angle range for kitchen appliances. To accomplish this, subjective ratings on visibility, physical comfort, and preference at various panel angles were collected through an experiment. Six different panel angles (0, 15, 30, 45, 60, and 90\({}^{\circ}\)) were tested, and the participants rated each measure using a 7-point Likert scale. The study results indicated significant impacts of panel angle on visibility, physical comfort, and preference ratings. For all three measures, the mean scores followed an inverted U-shape pattern as the panel angle increased: the panel angles ranging from 30 to 90\({}^{\circ}\) showed scores higher than or close to 4 (\"Neutral\"), with those of 45 to 60\({}^{\circ}\) exceeding 5 (\"Slightly agree\"). Conversely, the panel angle of 15\({}^{\circ}\) showed scores lower than 4 (\"Neutral\"), and that of 0\({}^{\circ}\) showed scores lower than or close to 3 (\"Slightly disagree\"). The effect of panel angle on visibility ratings appears to stem from the variation in the angle between the user's line of sight and the panel as the panel angle changes. This variation likely influences how difficult it is for the user to accurately view the power levels. Previous research suggests that optimal visibility and legibility are achieved when the display or panel is positioned perpendicularly to the user's line of sight [2; 4; 6; 39; 40]. However, this principle generally applies to standard display conditions, and for the knob panel considered in this study, additional factors had to be taken into account. The first factor is that, as seen in Figure 2, the power levels were marked closely around the knob on the panel surface (this is a common marking style in most knob panels on existing range products). Given the typical installation height of range products (800-900 mm) and the horizontal distance between the user and the product (set at 200 mm in this study), users tended to look down at the panel at an angle. Due to this viewing angle, part of the power level markings was obscured by the user's hand and forearm when grasping the knob, with this visual interference being more pronounced when the panel angle was shallow, such as at 0\({}^{\circ}\) or 15\({}^{\circ}\). The second factor is that the power levels were marked not only on the panel surface, but also on the side of the knob body. This allowed users to easily check the power levels even at steep panel angles, such as 90\({}^{\circ}\), by referencing the markings on the side of the knob. These two factors seem to have contributed to the experimental results, where panel angles between 30 and 90\({}^{\circ}\) achieved visibility scores higher than 4 (\"Neutral\"), with angles between 45 and 60\({}^{\circ}\) yielding particularly high visibility scores close to 6 (\"Agree\"). The panel angle's effects on the physical comfort ratings can be attributed to variations in the participants' postures, as the panel angle determines the angles of their wrist extension or neck/waist bending. In general, postural discomfort can arise if any joint angle exceeds its comfortable range of motion (ROM) [1; 2; 5; 18; 19]. Particularly, when adjusting the knob panel, users rotated the knob more than 300 degrees clockwise or counterclockwise depending on the desired power level. This action caused forearm supination/pronation, which, combined with wrist extension, can result in uncomfortable and awkward postures. According to [PERSON] et al. (2009), forearm rotation significantly affects wrist discomfort associated with wrist flexion/extension [41]. Specifically, wrist discomfort increases with wrist flexion/extension when the forearm is rotated (supination/pronation) compared to when it is in a neutral position. Indeed, a post-analysis of the video recordings collected during this study revealed that when the panel angle was flat, such as at 0\({}^{\circ}\), forearm pronation occurred while rotating the knob counterclockwise.