Xbar and R chart

The XBARR card is a kind of quality control chart.

Construction

The XBARR Card ( mean and range chart, x - cross -R 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 sampling range R.

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 the sample range 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 XBARR card can of course also be used in areas other than manufacturing. The advantage of XBARR card was for a long time that their leadership did not require complicated computational steps. With the advent of computer programs for statistical process control but this was no appreciable benefit more, and the use of XBARR card has become rare because the XbarS card, operating at the sampling standard deviations instead of sampling spans, is statistically more efficient.