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In statistical process control (SPC), the ¯ and R chart is a type of scheme, popularly known as control chart, used to monitor the mean and range of a normally distributed variables simultaneously, when samples are collected at regular intervals from a business or industrial process. [1]
Control charts are graphical plots used in production control to determine whether quality and manufacturing processes are being controlled under stable conditions. (ISO 7870-1) [1] The hourly status is arranged on the graph, and the occurrence of abnormalities is judged based on the presence of data that differs from the conventional trend or deviates from the control limit line.
In industrial statistics, the X-bar chart is a type of variable control chart [1] that is used to monitor the arithmetic means of successive samples of constant size, n. This type of control chart is used for characteristics that can be measured on a continuous scale, such as weight, temperature, thickness etc.
Use variable-width control limits [6] Each observation plots against its own control limits as determined by the sample size-specific values, n i, of A 3, B 3, and B 4: Use control limits based on an average sample size [7] Control limits are fixed at the modal (or most common) sample size-specific value of A 3, B 3, and B 4
In statistical quality control, the individual/moving-range chart is a type of control chart used to monitor variables data from a business or industrial process for which it is impractical to use rational subgroups.
The above eight rules apply to a chart of a variable value. A second chart, the moving range chart, can also be used but only with rules 1, 2, 3 and 4. Such a chart plots a graph of the maximum value - minimum value of N adjacent points against the time sample of the range.
[2]: 415 The chart monitors only the process mean; monitoring the process variability requires the use of some other technique. [2]: 414 The EWMA control chart requires a knowledgeable person to select two parameters before setup: The first parameter is λ, the weight given to the most recent rational subgroup mean.
Use variable-width control limits [2]: 280 Each observation plots against its own control limits: ¯ ¯ (¯), where n i is the size of the sample that produced the ith observation on the p-chart Use control limits based on an average sample size [2]: 282