X-bar chart

In industrial statistics, the X-bar chart is a type of control chart 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.

For the purposes of control limit calculation, the sample means are assumed to be normally distributed, an assumption justified by the Central Limit Theorem.

The X-bar chart is often used in conjunction with a variation chart such as the R-chart or s-chart. The average sample range, R, or the average sample standard deviation, s, can be used to derive the X-bar chart's control limits.