## 4 Conclusions  
1. The plane obtained as a result of measurements by the CMM machine is characterized by the smallest flatness error of value f = 61.9 \(\upmu\)m. Such accurate mapping of planes is an undeniable advantage of CNC machines. The obtained results confirm that the CNC machine is a device with high measurement accuracy. The results obtained from the CNC machine also feature the highest repeatability compared to results from the manual machine and the measuring arm. Due to its repeatability, the CNC machine began to achieve the repeatability of shape error measurements ranging from 55 to 65 \(\upmu\)m already with 60 collected measurement points. The slow movement speed of the CNC machine causes a significant increase in measurement time with an increase in the number of measurement points. To collect 60 measurement points, the machine needed about 23 min. An undeniable advantage is the possibility of automating the measurement process. This allows the use of staff trained only in operating the device for serial measurements.
2. The flatness error of the plane obtained using a manual machine was f = 63.6 \(\upmu\)m. The measurement time here is significantly better and amounts to approximately 13 min for measuring 100 points. This is the result of not needing to write a program to conduct the examination, which is significant for control in unit or small batch production. The actual measurement time for a single point is close to that of the automatic machine. A negative phenomenon is the lack of repeatability of parameters upon approaching a measurement point, which adversely affects the repeatability of the results. The machine needed as many as 100 points to achieve repeatability of shape error measurements in the range from 60 to 65 \(\upmu\)m. This is a consequence of the device being manually controlled by the operator. Additionally, a drawback of machine operation is the necessity to use trained personnel to conduct the examination.
3. Measurement using the measuring arm is the least precise, with the obtained flatness error of the plane at f = 0.0797 mm. Moreover, preparing the device for testing is a time-consuming operation. However, it is a device with high measurement speed. During the analysis of the obtained data, it was found that in the case of a small number of collected measurement points, the obtained measurement error deviates from the two previous methods, and the dispersion of results is significant. The measuring arm needed as many as 130 points to achieve repeatability of shape error measurements in the range from 77.5 to 82.5 \(\upmu\)m. The time needed to collect such a number of points is 17 min. With a greater number of collected points, the time proportionally decreases, and the repeatability of measurements also increases. To achieve satisfactory results, therefore, a larger number of measurement points should be collected, which, with high measurement speed, is not time-consuming. Measurements using the arm require the use of trained personnel. Despite the good balance of the arm, it also requires significant physical effort.
4. Summarizing the above results obtained using the aforementioned measurement methods, it can be asserted with certainty that, considering the difference in readings of 17.8 \(\upmu\)m between the final results obtained by the CNC machine and the measuring arm, the latter presents an interesting alternative to stationary machines. Measuring arms can successfully be used during the refurbishment works of large power machines. In doing so, they increase the accuracy of measurements of cooperating planes, reducing flatness deviations obtained in traditional measurements.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The authors declare no conflicts of interest.