XbarR card

The XbarR card is a type of quality control card .

construction

The XbarR chart (mean and range chart, x- bar R chart) contains sample data and two traces or graphs showing two sample parameters: the arithmetic sample mean ( ) ( read " X bar ", hence the name ; in German "x quer") and the sample range R. ${\displaystyle {\bar {x}}}$

The upper half, a quality control card (2nd part, the range card is missing!) ${\displaystyle {\bar {X}}}$

In practice, a sample often consists of 5 measured values. This can be, for example, the measurement results for five parts manufactured in direct sequence. For each sample, the sample mean and the sample range are then calculated and shown in the respective graphs. The resulting curves give the worker information about the stability of his process.

The XbarR card can of course also be used in areas other than manufacturing. For a long time, the advantage of the XbarR card was that it did not require any complicated calculation steps. With the advent of computer programs for statistical process control , however, this was no longer a significant advantage and the use of the XbarR card has become rare, because the XbarS card , which works with sample standard deviations rather than sample ranges, is statistically more efficient.

literature

• Edgar Dietrich, Alfred Schulze: Statistical procedures for machine and process qualification . Carl Hanser Verlag, Munich / Vienna 2005, ISBN 3-446-22894-2 .