A side-sensitive synthetic chart combined with an X chart

The synthetic chart combined with an chart (Synthetic- chart) signals when a sample point falls beyond the control limits or when a second point, not far from the first one, falls beyond the warning limits, no matter whether one of them falls above the centreline and the other falls below. The side-sensitive Synthetic- chart (SS Synthetic- chart) does not signal when the points beyond the warning limits are on opposite sides of the centreline. In this article, we show that the performance of the Synthetic- chart improves when it is side-sensitive; depending on the magnitude of the shift, the chart signals 30% faster.