## 4 Discussions
### Comprehensive Evaluation, Limitations, and Future Directions  
Unlike other objective evaluation methods designed for handwriting assistive devices, the method presented in this study offers a more comprehensive and detailed evaluation. For instance, assistive device [6] utilizes the Jebsen-Taylor Hand Function Test [15], which primarily assesses performance based on writing duration. Similarly, another assistive device [27] focuses mainly on evaluating the legibility of letters and the time required to complete writing tasks. In contrast, the method of this study evaluates both writing and drawing tasks, encompassing a total of ten indicators, from \(S_{1}\) to \(S_{10}\). This multi-faceted approach allows for a more thorough evaluation by capturing various dimensions of handwriting performance, such as pen pressure, pen angle variations, and structural organization. By integrating multiple indicators and evaluating both writing and drawing tasks, our method provides a holistic view of handwriting assistive devices, addressing limitations found in previous objective evaluation methods that tend to focus on singular aspects [6; 27].  
In addition, this objective evaluation method can significantly aid developers of new and innovative handwriting assistive systems and technologies. By utilizing the overall score generated from our method, developers can initially screen and compare different devices. Devices with higher overall scores indicate better performance across multiple aspects of handwriting. Furthermore, the detailed analysis of the ten objective indicators provides insights into particular areas where a device excels or requires improvement. The objective indicators can identify subtle deficiencies or performance characteristics that subjective evaluations might overlook, allowing developers to detect small details not apparent through subjective evaluation. Developers can focus on enhancing specific indicators with weights greater than 0.1, as these have a more substantial impact on the overall performance. This method allows for the efficient optimization of device design, ultimately leading to more effective handwriting assistive devices.  
However, several limitations of this study must be acknowledged. Firstly, the small sample size of ten participants may limit the generalizability of the findings. Additionally, although healthy individuals simulated using their non-dominant hand, it is impossible to fully capture the complex experiences of individuals with upper limb dysfunction. Another limitation pertains to handwriting on the tablet. Using a tablet and digital pen requires adapting to the screen's touch feedback and feel, which differ from the physical sensation of handwriting on paper. This necessitates a period of adaptation to handwriting on the tablet screen.  
Future studies will expand the sample size and involve actual users of handwriting assistive devices to validate the findings. We plan to collaborate with rehabilitation centers and hospitals to recruit participants with various types of upper limb dysfunction. Furthermore, if future improvements in tablet and digital pen technology make them more similar to traditional handwriting tools in physical and sensory properties, the evaluation method could provide more accurate results. Moreover, we envisage adapting the evaluation method for different languages and writing systems to broaden its applicability. While currently used for evaluating assistive devices for individuals with upper limb dysfunction, this method has the potential to be applied to the evaluation of handwriting ability in a broader population, such as children with handwriting difficulties and elderly people with decreased muscle strength. By extending our research to these areas, we aim to contribute to the development of more personalized and effective handwriting assistive technologies.