## 2 Materials and Methods
### Preprocessing & Data Analysis
The mean error (ME), which is the average of the time series pair's difference, can conclude the occurrence of bias but at a granular level, for example segments of the exercise. However, aggregation of the ME is prone to involve effects such as error cancellation. The ratio of ME and MAE, for instance \(\frac{\text{ME}}{\text{MAE}}\), draws insights into the occurrence of systematic bias (Figure A4). A value close to \(\pm 1\) implies less tendency of ARKit to fluctuate around the Vicon's angle estimation, for example either under-, perfect- or overestimation takes place. Values nearby zero indicate the ME's cancellation effect \begin{table}
\begin{tabular}{c c} \hline \hline
**Angle** & **wMAE** \\ \hline leftElbow & \(24.0^{\circ}\pm 17.43^{\circ}\) \\ leftHip & \(16.91^{\circ}\pm 10.67^{\circ}\) \\ leftKnee & \(16.61^{\circ}\pm 7.47^{\circ}\) \\ leftShouder & \(20.01^{\circ}\pm 14.89^{\circ}\) \\ rightElbow & \(20.0^{\circ}\pm 15.32^{\circ}\) \\ rightHip & \(20.17^{\circ}\pm 11.25^{\circ}\) \\ rightKnee & \(17.57^{\circ}\pm 7.25^{\circ}\) \\ rightShouder & \(17.39^{\circ}\pm 12.18^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The aggregated wMAE values for all joint angles. Figure 3: Shift of the data. (over- and underestimation) but require further analysis, such as the difference between MAE and ME, for conclusions. One-way analysis of variance (ANOVA) is performed to quantify the effects of the categorical metadata such as angle (fixed effect), exercise (fixed effect), and subject (random effect), on the continuous variable MAE. The random effect was taken into account performing one-way ANOVA using a random effects model. The distribution of MAE shows a divergence towards the normal distribution, which is one of the requirements in ANOVA. However, research verified robustness in violating this assumption in certain bounds [47]. A logarithm (basis 10) transform on the MAE variable ensures stronger normalization (Appendix A, Figure A1). In particular, it makes the model multiplicative and more robust to dispersion. The visual inspection of histograms reveals a lack of homogeneous intergroup variance and motivates to apply [PERSON]'s ANOVA. Finally, the Games-Howell post-hoc test [48] compares the individual categorical factors for significant results (here defined as an effect size larger than 0.1). Besides view (frontal or side), the binary independent variables are the body segment of the angle (lower or upper) and information on the movement of the pelvis. The latter is declared as the variable center moved and indicates whether the proper execution of the exercise involves the movement of the pelvic's center, the origin of the ARKit coordinate system. To quantify the binary variables' effect, we fitted a logistic regression model based on the MAE and applied [PERSON]'s \(t\)-test. The results, including \(\beta\) coefficient, \(R^{2}\)\(p\)-value, and confidence interval, are compiled in a table. Assumptions about the data are made and can restrict the interpretation of the results. A more detailed outline of this topic is given in the limitations section (Section 5.8).