## 3 Results and Discussion
### Analysis of Variance and Regression Analysis
This reduces the amount of energy in the process of decomposing the material below its surface by increasing the cutting speed, as well as increasing the amount of energy on the board surface. Therefore, it is clear that it increases the area affected by heat due to energy excess on the board surface, which is consistent with the results of [PERSON] and [PERSON], [84; 85]. The width of the heat-affected zone increases as the power of the laser P increases, as [PERSON] [7] also pointed out. If we also take into account the factor AR, then its effect on WHAZU\({}^{*}\), although also negligible, is directly proportional. All model quality indicators improved after the inclusion of interactions in the model WHAZU\({}^{*}\), but not so significantly that we can consider this model as credible. However, we can use it to explain the influence of the investigated factors and their interactions on the investigated response, in this case, WHAZU\({}^{*}\). The mutual interaction between the laser power P and the cutting speed V determines the degree and form of energy distribution, as in the case of the WKU\({}^{*}\) or WHAZU\({}^{*}\); this causes the wood chemical decomposition and thus determines the width of the heat-affected area. The cutting speed also affects the properties at the same time, and in particular, the distribution of the flowing auxiliary gas on the board surface. It follows from the results of the analysis of variance for the transformed values of the cutting kerf width on the board bottom of the WKD\({}^{*}\) that the influence of the cutting speed factor V, the laser power P, and the factor AR is statistically significant. These results are in harmony with [PERSON] [79]. The reason for this is again that the wood thermal conductivity plays an important role in heat transfer in the phase of penetration of the energy beam into the material, while on the surface, respectively in the phase of energy contact with the board surface, the surface properties of wood are manifested analogously, as in the case of WKU\({}^{*}\) and WHAZU\({}^{*}\). It is clear that the cutting speed V increase, as well as the density increase, and respectively the number of annual rings AR, results in a reduction in the cutting kerf width on the board bottom. The results correspond to the results of [PERSON] and [PERSON] [57] or [PERSON] and [PERSON] [45; 49] in a cutting depth analysis. On the contrary, an increase in the power P of the laser results in an increase in the value of the cutting kerf width WKD* on the board bottom, which is in accordance with the published results, e.g., [PERSON] et al. [47]. It was found, by comparing the effect of the factors for both widths WKU* and WKD*, that the power factor P and the speed factor V act in the same direction on the width values of the WKU* and WKD*. However, the factor AR, respectively the wood density, acts to increase the cutting kerf width on the board surface, in contrast to the effect on the board bottom, where it reduces this width by its influence. The extent value of the variance explanation only improved insignificantly in the case of the interaction model for WKD*, so the model without interactions sufficiently and simply describes the influence of the factors P, V, and AR on WKD*. The effect of the factor AR could not be confirmed by the results of the variance analysis for WHAZD*; however, a significant effect was confirmed by the cutting speed factors V and laser power P. It is clear that the value of WHAZD* increases with an increasing laser power P and, conversely, the value of the width of the heat-affected zone on the surface of the board bottom decreases with an increasing speed V. It follows from the results of a detailed analysis that a significant improvement in all properties of the model will not be achieved, even when considering the interactions between the investigated factors. Considering this, it is necessary to include other factors in the analysis in the case of continuing research, e.g., the auxiliary gas flow rate.