## 4 Discussion
The most common include errors due to shrinkage of the material, an error resulting from the fact that not all of the radiation falls on the matrix at exactly 90 degrees, and from radiation scattering which results in the formation of a UV light bleed, which acts on the material outside the contour of the mask to cure it [34]. This results in a mechanism that is intuitively easy to explain, in which the longer the exposure time, the more resinmanages to cure outside the contour. This is also how errors arise, causing the printed holes to be smaller than the nominal dimensions and the effect of shrinkage, and the outer dimensions to be 3D printed larger. If the holes are relatively small, this leads to plugging. Analyzing the topic a level deeper, it is not hard to see that illumination time alone is a vague parameter in the context of curing photopolymers. What matters is the amount of energy that must be delivered to cure the resin. Thus, it is important that the entire working area be as evenly illuminated as possible to be able to obtain reproducible 3D printing results regardless of where the object is located on the printing platform. Therefore, it is first necessary to calibrate the illumination intensity of the UV matrix. In this study, such calibration was performed by measuring the distribution of UV intensity on the LCD matrix and an in-house method of analyzing the measurement data leading to the generation of a grayscale mask that can be used to darken the matrix locally, minimizing local irregularities in the intensity of UV radiation curing the resin. As a result, more predictable printing was achieved, which also improves calibration accuracy. Although the shrinkage value is declared by the resin manufacturer in the specification, this value is not useful for dimensional correction, as the manufacturer usually declares volumetric shrinkage [34]. When minimizing dimensional and geometric errors in models made using the mSLA method, a more linear shrinkage value is needed. Although this value can be theoretically recalculated according to Equation (7), in practice it is better to determine it experimentally. As shown in the conducted studies, the material displacement associated with shrinkage significantly varies depending on the geometry of the model. \[S_{l}=1-\left(1-S_{v}\right)^{1/3} \tag{7}\]  
where \(S_{l}\) is linear shrinkage [-] and \(S_{v}\) is volumetric shrinkage [-]. In order to compensate for shrinkage at the slicer stage, a shrinkage study based on the displacement of markers on the test model was proposed. The markers, for which their center is determined, allow one to determine directly the shrinkage value without mathematical elimination of the light bleed effect. This way, errors do not accumulate, so calibration is simpler and more predictable. In order to measure the coordinates of the centers of the markers with the required accuracy, measurements were carried out using the iNexive vision system. Future research can be developed toward using simpler image acquisition and image analysis methods to automate this process. The discussion presented also mentioned the occurrence of UV light bleed, also curing the resin outside the mask outline. Recent studies have confirmed that the phenomenon of light bleed significantly affects the dimensional accuracy of models printed using the mSLA technology and related methods [28; 34; 35; 36; 37]. In the research conducted, it was assumed that the effect of light bleed on the inner and outer contours has opposite direction. As a result, the outer dimension is reduced by shrinkage while being increased by light bleed. The inner dimension, on the other hand, is reduced by both shrinkage and light bleed. It is this difference that results in dimensional error asymmetry. Errors due to shrinkage depend on the value of the nominal dimension, so their compensation should be carried out by means of a scale factor. The effect of light bleed, on the other hand, is independent of the size of the detail, and thus cannot be fully compensated for by scaling.