Control charts are bar charts that are plotted based on specific measurement data of product or process performance at different time intervals. They allow us to consider the dynamics of changes in indicators, and due to this, in the future, control the process itself.
Instructions
Step 1
Control charts differ from ordinary ruled charts only in additional horizontal lines. These lines indicate the control limits (upper and lower) of statistically acceptable changes in the considered or measured value, as well as the average size of all measurements.
Step 2
Draw the top and then the bottom of the graph. To do this, create a line of average values, and then identify certain (maximum permissible) boundaries of these values in the form of the maximum possible decrease in the indicator under consideration and an increase.
Step 3
Note the changes in the value in question on the graph. Points, which are plotted in the form of changes on the control chart, can be formed not only as a result of direct measurements of a specific indicator of the process, but also as a result of the total value of a group of certain indicators that were obtained in the same period of time. For example, this cumulative metric might include the average size for a group of measurements, the deviation value, the average value of defects per unit of production, and the percentage of defects.
Step 4
Determine the change in the indicators on the control chart over time. This way, you can know exactly when and how the process change happened and thus develop a basis for further management of it. For example, if the control chart shows some single case of a value going beyond the control limits, then there is no need to take any action to correct the process in question. But if the control chart reflects an asymmetric shift of the indicator under consideration (over a long period of time) with respect to the line of the mean, then this process requires urgent intervention and the adoption of certain corrective actions.
