Quality is a vital element in every field. In order to compete among the competitors, the manufacturer or service provider should produce or provide quality product or service. However, before a product or service can be considered as having an acceptable quality level, all the processes producing the product (or providing the service) should be in-control. The synthetic X chart consists of two sub-charts, i.e. the X /S sub-chart and CRL/S sub-chart. The synthetic X chart is used to detect

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... s in the process mean. In this paper, we study the percentage points (percentiles) of the run length distribution of the synthetic X chart so as to provide practitioners with a more complete understanding of the behaviour of the chart, instead of the sole dependence on the average run length (ARL). Index Terms-Average run length (ARL), conforming run length (CRL), run length distribution, synthetic X chart.