# Xbar and s chart

The XbarS card is a kind of quality control chart.

## Construction

The XbarS Card ( mean and standard deviation map, x - cross -s card) contains sample data and two tracks or graphs in which two sample parameters are shown: the arithmetic sample mean () ( read in English " X bar", hence the name, in German " x bar ") and the sample standard deviation s

In the production practice, a sample often consists of five readings. This can be, for example, the measurement results for the five made in direct sequence parts. Then the sample mean and sample standard deviation are calculated and shown in the respective graphs for each sample. The resulting curves give the workers information about the stability of his trial.

The XbarS card can of course also be used in areas other than manufacturing. In the era of manual control charts guide the use of XbarS card was rare because the manual calculation of the standard deviation was quite cumbersome and error-prone; Instead, it was worked primarily with XBARR card that requires only the calculation of range values. With the advent of computer programs for statistical process control but this was no appreciable benefit more, and the XbarS card is because of their greater statistical efficiency today the standard means of monitoring of measurable features.