## 4 Conclusions  
In general, control charts are considered a proven means of improving the quality parameters of production and preventing errors - discrepancies in production. Industrial practice values the control charts because of their preventive nature. They help prevent unnecessary adjustment of equipment, production lines if the technological process is stable. In addition, they provide ongoing diagnostic data on process variability and make it possible to obtain information on monitored processes' capability. In industrial practice, control charts contribute to optimizing economic aspects (i.e., to the overall reduction of control costs). Production quality control using control charts is used especially in repeated processes when under relatively stable production conditions (i.e., technology, material, technical parameters of machines and equipment) there are other influences (i.e., small deviations from prescribed technology, small deviations in material quality, small inaccuracy of setting parameters of machines and equipment). Significant non-exceedance of effects will manifest itself within certain \"reasonable\" limits as a random effect. [PERSON] emphasized the empirical usefulness of the control chart for recognizing deviations from the state in which the technological process is statistically mastered. Measurement control charts are suitable for several reasons. Most technological processes and the above-mentioned drilling process, with their inputs and outputs, provide measurable features so that their wide use is possible. In the practical application, it was considered that the behavior of the technological process of drilling could be analyzed regardless of the technical specification. The charts reflect the technological process of drilling and give an image of what the process itself is capable of. In industrial practice, the stabilization of the process also contributes to shortening the time difference between an unstable technological process and corrective intervention. The behavior of the measured values and the limits determined on the basis of the control characteristics give a sufficiently reliable visual image of the course of the measured values themselves. Thus, it is possible to evaluate the measured data in real time and provide the measured variables' current state. By their action, the sought systematic causes cause a fundamental change in the variability or position of the process, whereby the process ceases to be in a stable state. From the control charts, it can be stated that the foreseeable systematic causes of instability of the drilling process are probably caused by wear of the drilling tool, high flushing water pressure, insufficient fixing of the drilled rock sample. The impact of these causes can be reduced by early intervention, but it is not possible to completely eliminate their occurrence without technological changes. Unforeseeable systematic causes cause significant changes in the technological process. They can be prevented. Typical such causes in the drilling process are the breakage of a drilling tool, the fall of a diamond from a drill bit, an improperly chosen working mode with respect to the rock being disintegrated, an uncontrollable oscillation of the drilling equipment, lack of knowledge of the drilling process and the human factor. It was stated that the \(R\)-chart reveals undesirable fluctuations within the subgroups of technological parameters and is an indicator of the magnitude of variability of the observed technological drilling process. The individual \(\vec{x}\), \(s\), \(\vec{\pi}\)-control charts show that the technological drilling process is off-center and unstable for the input parameters as revolutions, pressure force, and output parameter vibration signal. At revolutions and vibration signal, the periodic character of the measured quantity is clearly manifested. In the pressure force, inappropriate time trends appear.