## 4 Discussion
### Instrumentation Considerations  
Our findings suggest that some important technical characteristics of the data capture instrumentation must be considered to minimize propagated errors in biomechanical features in handwriting, drawing, or tracing studies. In this study, erroneous segmentation in the validation dataset could partially be attributed to the tablet's variable sampling rate. While most studies have presumed a fixed sampling rate, others have reported different rates during data collection [21] or have omitted this information altogether [3; 5; 28]. For the current study, the sampling rate variability could be attributed to the connection between the server and tablets. While a variable sampling rate may be inherent to the systems used for data acquisition and, thus, unavoidable, this variability could negatively affect common features, such as fluency, entropy, or essential tremor, in the study of handwriting complexities [3; 10; 29]. For example, if one assumed a constant sampling period between data points when, in fact, the sampling period varied, then all instantaneous measures, such as velocity, that depend on time differences between samples would be inaccurate. Those errors would propagate to derived measures, such as fluency, and would, in turn, be further magnified in any cognate summary statistic, such as average acceleration.  
The sampling rate itself is also an important consideration. For example, essential tremor is found to be between 4-12 Hz [29], requiring a minimum sampling rate of 24 Hz to accurately capture this behavior. A low sampling rate may compromise the detection of within-brushstroke pauses, which have been proposed as an important measurement for categorizing divergent drawing or handwriting capabilities [11; 30]. Most studies reporting high (100-200 Hz) sampling rates have used specialized WACOM drawing tablets [4; 13; 20; 22; 25]. Studies deploying consumer-based tablets, such as the iPad with an Apple Pencil, report a much lower sampling rate of 60 Hz [1], or a Samsung tablet with an unspecified sampling rate [28]. Thus, when using cost-effective, consumer-grade tablets, special attention must be paid to the sampling rate and its consistency over time, and, consequently, the kinematic features that can be reasonably estimated.  
Touchscreen technology is another important consideration. Specifically, our findings indicate an effect of hand position on brushstroke segmentation when using consumer-grade tablets outfitted with capacitive screens. Functionally, capacitive screens do not directly measure pen pressure. Rather, they register pen position based on contact with an electrical conductor such as a stylus pen tip or hand. As the current study demonstrated, pen proximity as well as the hand resting on the screen contributed noisy data points that distorted brushstrokes, which, in turn, could propagate to incorrect feature measurements. Since capacitive screens are inherently sensitive to pen proximity and hand position, it is plausible that the same effects were present in other studies using similar hardware. Therefore, it is critical that future studies consider denoising methods, such as the one proposed here, for removing spurious data points.