## 1 Introduction
Thus, energy density must be calculated by the equation, which consists of the beam overlay ratio \(x\), which includes the hatch distance and laser beam diameter:  
\[ED=\frac{P}{v\cdot HD}\cdot x \tag{1}\]  
where \(ED\) [J/mm\({}^{2}\)]--energy density, \(HD\) [mm]--hat distance, \(v\) [mm/s]--laser beam speed, \(P\) [W]--laser power, and \(x\)--beam overlay ratio, which is calculated according to the following:  
\[x=\frac{d}{HD} \tag{2}\]  
where \(d\) [mm]--laser beam diameter, \(HD\) [mm]--hat distance. On the _Formiga P100_ (manufactured by EOS GmbH--Electro Optical Systems, Krailling, Germany) machine where measurements were conducted, \(d\) is constant (\(d\) = 0.42 mm). Numerous factors in SLS affect mechanical, thermal, and rheological properties, roughness, and dimensional stability. Some parameters, like laser power, hatch distance, laser diameter, and scan speed, which are all combined by Equation (1) into energy density, are widely regarded by many authors as the most important in this context. Because of the orthogonal trajectories of the laser beam during exposure, different orientations of the samples in the \(xy\) direction may lead to different mechanical properties. Thus, [PERSON] et al. [13] found that the orientations of \(0^{\circ}\), \(30^{\circ}\), \(45^{\circ}\), and \(90^{\circ}\) do not significantly affect the tensile strength. The influence of orientation, power, and hatch distance on tensile strength showed that changing the orientation in the \(xy\) axis of the test specimens by \(45^{\circ}\) and \(90^{\circ}\) relative to \(0^{\circ}\) resulted in decreased values. However, when the laser power was at its peak, values around 27 MPa were achieved [14]. [PERSON] et al. investigated various hatch strategies and found that alternately hatched specimens showed an increase in tensile strength. A maximum tensile strength of 50 N/mm\({}^{2}\) was achieved [15]. According to the given Equation (1), [PERSON] et al. found that varying energy densities impact the tensile properties of polyamide 12 made by selective laser sintering. Results from tensile testing show that the implementation of a skin/core configuration allows the production of SLS parts with a valuable set of properties, minimizing the trade-off between mechanical strength and overall accuracy [16]. Furthermore, it is necessary to highlight the work of [PERSON] et al., in which they determined the influence of processing parameters (laser power, scan speed, hatch distance, and scan length) on key mechanical properties (strength, modulus of elasticity, and elongation) of PA12 printed parts using the response surface methodology. The results showed that hatch distance is a major influencing factor in mechanical properties [17]. In our practice, it has been shown that when making products at different levels in the working chamber (looking at the height along the \(z\) axis) with selective laser sintering, deviations in dimensions occur, and when working at higher levels, the deviations are higher. Accordingly, the research in this paper is focused on the comparison of dimensions at different levels in the chamber through statistical analysis in the software Design Expert ver.13 (Manufacturer Stat-Ease, Minneapolis, MN, USA). There are not many works that compare the dimensions at various levels along the \(z\) axis in the working chamber, because most often they try to reduce costs, and due to the very logic of laser sintering in the SLS process, the chamber is filled along the \(x\) and \(y\) axes and then in the \(z\) axis. Furthermore, in accordance with the reviewed literature, hatch distance is the most influential parameter in the total energy density, and it was taken along with orientation as input parameters in both levels. In addition to the dimensions, the influence of the mentioned parameters in the upper and lower parts of the working chamber on the tensile strength was also tested.