## 4 Discussion
The safety margin is also influenced by the static COF [63], such that it will be high in the case of slippery object as in copper alloy used in our experiment. The pinch-pulling force relationship can be used as an assessment for pinch force control against unpredictable loading for stroke patients. The CV value (represented by standard deviation divided by the mean) indicates how well the mean values of pinch and pulling forces summarizes the whole dataset. Interpretation of CV may vary; the rule of thumb can be used, which states the CV value of under 1 shows a small variance [64]. In this study, the CV values were 0.248 and 0.35 for pinch and pulling forces of the right hands, respectively. The CV values were 0.241 and 0.31 for pinch and pulling forces of left hands, respectively. Hence, the mean pinch and pulling force values are a reasonable representation of healthy adults in Malaysia. The results also indicate that the pinch and pulling force vary among the volunteers at the slip onset, which is expected as each volunteer has a different body size, hand size, and amount of safety margin. For instance, a bigger fingertip size leads to a larger contact area between the fingertip and the object's surface. Consequently, larger contact area would lead to larger pinch force, as reported in a related study by [PERSON] et al. [65], who showed that there is a positive association between contact area and force exerted by the index finger. In addition, each volunteer has different skin characteristics such as oiliness, moisture, roughness, and age that may affect the friction between fingertip skin and pincer object's surface. In this study, the mean static COFs for right and left hands were computed as \(0.518\pm 0.146\) and \(0.517\pm 0.145\), respectively. This is relatively consistent with previous findings related to measuring COF between human skin and copper material, reported by [PERSON] et al. [66] (mean COF = 0.55) and [PERSON] et al. [67] (mean COF = 0.58). In the literature, many studies have reported a significant difference in maximum pinch force between right and left hands [68]. Although our results show a slight increase in the means of pinch and pulling force for right hand compared to the left hand, there was no significant difference (\(p>0.05\)). Thus, it is not required to distinguish between right and left hands when a single-gender group is recruited for further research. Furthermore, the unaffected hand can be used as a reference for the affected hand during the rehabilitation of post-stroke patients. The explanation of this result can be that the volunteers did not exert their maximum pinch force at the slip onset. This is consistent with a study conducted by [PERSON] and [PERSON] [69], who reported that there is no significant difference between left and right hands when the grip force is at 25%, 50%, and 75% of the maximum force. The results of their study indicate that there is a significant difference only at maximum grip force. Recently, three main components of the assessment system are required for an assessment system to be fully automated: administration, data acquisition, and rating [19]. Administration involves the instructions and procedures to evaluate the patient, while the data acquisition involves obtaining the outcome measurements from patients. Rating is the criteria to evaluate the outcome measurements of the patients, which are usually designed as an ordinal scale. In this study, only the pinch data acquisition system is automated based on UE-FMA protocol. The limitation of this study is that the administration and rating components are not yet automated. In the future, this limitation will be addressed, such that stroke patients with pinch deficits at different levels of impairment (severe, moderate, and mild) will be recruited to determine the threshold values for each level so that an automated rating process can be performed.