# Estimating the Uncertainty of Measurements for Various Methods and 3D Printed Parts
## 4 Discussion
Analyzing Figures 11 and 12 on the effect of the number of samples tested on the value of the result and its statistical interpretation, it can be concluded that in both the variants without and with seam, the average value of the diameters decreases with the increase of the analyzed population and stabilizes at a similar level already for 20 analyzed samples. The largest difference occurs for the test with seam using 3D scanner measurement. Tables 3 and 4, for all samples tested and the methods used, clearly show that for 20 samples, the average values have the same values as for the measurement of all 30 samples. Moreover, not only the average value stabilizes with 20 tested samples, but alsothe expanded uncertainty. In the case of Figure 12 (seamless measurement) and the corresponding Table 4, the average values for 20 and 30 samples have the same values: 15.03 mm (caliper) and 15.02 (CMM), and the difference in the expanded uncertainty between both series is only 0.02 and 0.03 mm, respectively. Comparing the expanded uncertainty values for a series of 10 and 20 measurements, these differences are 0.07 mm (caliper) and 0.04 mm (CMM), respectively. The quantitative interpretation of the test results for measurements depending on the number of samples is shown in Tables 3 and 4. In Table 3, where the results of tests for samples with seam using Dial Caliper are presented, it can be clearly seen that as the number of samples tested increases, not only the average value of the measurement decreases, but also the expanded uncertainty, which is for the analyzed measurement methods and sample sizes respectively: n-3, U\({}_{\rm CA}\)-0.029; n-30, U\({}_{\rm CA}\)-0.008. As can be seen, the actual U\({}_{\rm CA}\) value considering the measurement from 30 samples with seam is almost 3.5 times lower than for the series of three samples analyzed. The same characteristic styles can be seen when analyzing the data in Table 4, where the results for Dial Caliper were n-3, U\({}_{\rm CA}\)-0.018; n-30, U\({}_{\rm CA}\)-0.006. As can be seen, the actual U\({}_{\rm CA}\) value considering the measurement from 30 samples without seam is 3 times smaller than for the series of three samples. In the case of CMM for measurement with and without seam, an identical trend can be seen, where, however, the differences in the value of the expanded uncertainty depending on the number of analyzed samples differ for the measurement with seam more than twice, and for the measurement without seam-three times. It seems that the application of good measurement practices should take into account the minimum statistical number of samples in accordance with the adopted statistical principles at the level of 30 samples. In the case of the presented test results for 20 samples, there was a satisfactory stabilization of both the average diameter value and the expanded uncertainty. Good measurement practice should take into account whether the measurement was carried out at the seam or not, and how the measurement method, and measurement strategy, was selected. The measurement strategy should take into account the nature of the surface, the selection of appropriate sensors, measuring jaws, etc., which affect the average value, as shown by the results for 3D scanning, which are not sensitive to the influence of the measuring probe tip. Each time, the scanner measures the entire surface, including the seam, but also the valleys occurring at the junction of the layers, which is not obvious in the case of mechanical contact measurements. Based on the evaluation of the influence of the number of samples on the final measurement result, it can be concluded that the interpretation of test results carried out for a small number of samples, despite the statistical calculations carried out, gives a completely different final result both regarding the average value and in terms of statistical evaluation.