## 4 Discussion  
As functional models are often produced using additive technology, it is necessary to develop guidelines for optimizing 3D printing parameters to create models that meet the requirements for dimensional and shape accuracy and surface roughness. For this purpose, ISO/ASTM 52901 [29], ISO/ASTM 52902 [30], and ISO/ASTM 52910 [4], among others, have been developed. However, the information in the presented standards provides only general guidelines for verifying the accuracy of 3D printers, which in no way directly relate to establishing calibration parameters for 3D printing models also obtained using the mSLA method. Therefore, it was necessary to develop, within the framework of the presented publication, a procedure related to the calibration of a 3D printer using, among other things, individually designed models to establish parameters minimizing manufacturing errors. For the mSLA method, in particular, it is important to choose the right exposure time [31] and layer thickness [32] of 3D printing. In general, the layer thickness is determined according to the recommendations of the resin manufacturer or the type of 3D printer. In practice, it is believed that the value of the layer thickness below 30 \(\upmu\)m, does not bring tangible benefits, and unnecessarily increases the time of making the model. Therefore, in the presented research, we maintained the recommended value given by the manufacturer. According to this recommendation, for the mSLA Anycubic M3 Premium 3D printer, the 3D printed layer thickness should be 50 \(\upmu\)m. The problem is more complex in terms of determining the correct exposure time. So far, no clear recommendations have been made for determining the value of this parameter. Recommendations contained in publications and provided by manufacturers are usually very general [15; 16; 31]. The authors of the publications mainly aim at adopting such a value of the exposure time that the 3D printing layer will achieve adequate strength while not curing too deep into a single layer. Determining such a value of exposure time also avoids the overcuring of higher layers, which would lead to excessive increase in stress, brittleness and increase in dimensional and geometry errors [33]. Commonly available calibration models and calibration instructions are mostly based on subjective evaluation of the detail and strength of prints by observing the fine details of test prints [20; 21]. However, there is a lack of description of calibration methods based on measurements that give numerical comparison data. In the case of the publication presented here, the authors used two models, one of which was used to evaluate the detail of the print and the other for its strength. The criteria for evaluating the print detail on these models are clear and easy to apply. The preferred exposure time can then be determined based on the optimization criterion. The published literature lacks a comprehensive calibration procedure for 3D printers that utilize the mSLA method [15; 16; 31]. This paper presents a calibration procedure that includes several key elements: testing the uniformity of UV intensity emitted by the LCD matrix of the Anycubic M3 Premium printer using a grayscale correction mask, determining the optimal exposure time, and assessing the linear shrinkage of samples. One notable advantage of the method presented is its ability to collect and analyze numerical data, reducing the impact of the operator's subjective judgment--which is often a significant factor in traditional calibration methods. Until now, most verification methods for models created using the mSLA technique have relied solely on visual evaluations, which depend heavily on the operator's subjective assessment [15; 32]. Geometric errors in models made using the mSLA method can result from a variety of factors.