During the production process, selective measurements of products are carried out. After that, the graph and diagrams of the variability of sample values of planned specifications in samples are constructed, and the degree of their proximity to the set values is considered (Avram, 2022). If the charts detect the presence of a trend of sample values or it appears that the sample values are outside the specified limits, then it is considered that the process is out of control, and the necessary actions are taken to find the reason for its breakdown (SPC Exel, 2021). The values of sample averages are plotted on the Xbar chart to control the deviation of a continuous variable from the average value. The values of the sample ranges are plotted on the control R-chart to control the degree of variability of the continuous parameter.
This example demonstrates the control chart of the correct process. The points on the diagram are inside the control limits. At the same time, there are no systematic shifts (trends) or other signs of the process getting out of control. The points of the chart fluctuate uniformly, at least based on visual analysis, relative to the corresponding average lines.
References
Avram, D. (2022). X-bar and r-chart: Is there a difference and how are they used? AlisQI.
SPC Exel. (2021).Comparing XBar-R and XBar-s control charts. BPI Consulting.