## 4 Discussion  
The presented description of the method of describing a set of points with elliptical areas can be implemented to describe the results of operational tests in which the test \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**PM 2.5** & \(a\) & \(b\) & \(\alpha\) & \(x_{COG}\) & \(y_{COG}\) & \(\Delta_{P}\) & \(k\) & \(A\) \\ \hline \(\mu\)g/m\({}^{3}\) & m & m & \(\circ\) & m & m & - & \% & m \\ \(<\)23 & 8.43 & 8.33 & 7.90 & 8.71 & 9.05 & 0.61 & 82.7 & 220.50 \\ \(<\)20 & 8.26 & 8.26 & 6.17 & 8.79 & 8.97 & 0.58 & 82.6 & 214.21 \\ \(<\)17 & 8.69 & 8.55 & 18.00 & 9.21 & 8.83 & 0.59 & 88.2 & 233.63 \\ \(<\)14 & 6.84 & 4.05 & 19.10 & 4.79 & 2.01 & 0.79 & 79.3 & 87.10 \\ \(<\)11 & 2.44 & 0.50 & \(-\)2.94 & 3.01 & 0.77 & 0.31 & 87.5 & 3.87 \\ \hline \(\mu\) & 6.56 & 3.83 & 10.47 & 6.45 & 5.15 & 0.57 & 84.4 & 134.70 \\ \(\sigma\) & 2.86 & 3.83 & 10.47 & 3.04 & 4.37 & 0.20 & 4.2 & 108.77 \\ \hline \end{tabular}
\end{table} 
Table 4: List of parameters describing dimensions of areas with different values of PM 2.5 particulate matter concentration, where \(a\)—semiavis of the ellipse parallel to the direction line, \(b\)—semiavis of the ellipse perpendicular to direction line, \(\alpha\)—angle of inclination of the direction line, \(x_{COG}\)—position of the center of the ellipse on the horizontal axis, \(y_{COG}\)—position of the center of the ellipse on the vertical axis, \(\Delta_{P}\)—uniformity ratio of points’ distribution in relation to the mean value of the radius vector for the points of the analyzed set, \(k\)—percentage of points located inside the area defined by the ellipse, and \(A\)—area of the plotted ellipse. Figure 10: Graph showing muscle activity values during propulsion of a manual wheelchair dependent on the value of the moment of resistance to motion for different assistance gain factor values w from the electric motor assistance system. results can be presented on two-dimensional graphs. The axes of these graphs may present any units, which is confirmed by the provided examples of method applicability. The application of the method is shown on data obtained during tests measuring the emissions of the internal combustion engine and the muscular activity of the human-wheelchair anthropotechnical system during the propulsion of the push drive. When implementing the method for individual measurement results, one should note that the values presented on the horizontal and vertical axes are of the same order of magnitude because, otherwise, inaccuracies may arise in mapping the set of points with an ellipse. This was noted in the applied example of the muscle activity tests. In this case, the original muscle activity values were expressed as a percentage; therefore, the measured effort ranged from 0 to 1. However, assuming such a size interval on the vertical axis resulted in excessive elongation of the semiaxis a. Because of that, the muscle activity value \(MVC_{max}\) was converted into a percentage value ranging from 0 to 100%. A better ellipse-shaped representation of the area of the measured points was obtained by doing so, and the location of points was determined by the values of the resistance moment on the horizontal axis and by the muscle activity \(MVC_{max}\) on the vertical axis. The results of muscle activity of disabled wheelchair users implemented in the verification are characterized by a similar range of findings as in articles analyzing these results in terms of other aspects [49; 50]. When applying the method, the uniformity of distribution for the set of analyzed points with respect to the mean value is important. This uniformity is defined using the uniformity ratio \(\Delta P\) of the distribution of points with respect to the mean value of the radius vector of the points in the analyzed set. The effect of the \(\Delta P\) coefficient was particularly noticeable when analyzing the PM 2.5 particulate matter emission areas.