R charts are control charts for _______.

Explanation:

Control charts:

• A control chart is a graphical representation of the collected information.
• It indicates whether a process is in control or out of control.
• It determines process variability and detects unusual variations taking place in a process.
• It ensures the product quality level.
• It provides information about the selection and setting of tolerance limits.

Types of Control Charts:

Variable charts are meant for the variable type of data. X bar and R Chart, X bar and sigma chart, the chart for the individual units

Attribute charts are meant for attribute type of data. p chart, np chart, c chart, u chart, U chart.

Control charts for the variable type of data (X bar and R charts)

• In the x bar chart, the sample means are plotted in order to control the mean value of a variable.
• In the R chart, the sample ranges are plotted in order to control the variability of a variable.

R charts:  

• R charts are used to monitor the variation of a process based on samples taken from the process at given times (hours, shifts, days, weeks, months, etc.).
• The measurements of the samples at a given time constitute a subgroup.

Additional Information 

Control charts for Attribute type data (p, c, u charts)

• p-charts calculates the percentage defective in the sample; p-charts are used when observations can be placed in two categories such as yes or no, good or bad, pass or fail etc.
• c-charts counts the number of defects in an item; c-charts are used only when the number of occurrences per unit of measure can be counted such as the number of scratches, cracks etc.
• u-chart counts the number of defects per sample; The u chart is used when it is not possible to have a sample size of a fixed size.