Explanation: Signal Resistance is a very important property of any control chart. It is defined as the maximum standard deviation of the sample mean from the target or in-control value, not leading to an immediate out-of-control signal.

Where L is the multiplier used to obtain the control limits.

Explanation: The Shewhart control charts have the signal resistance value equal to the multiplier used to obtain the control limit, which is constant. As a x chart is also a Shewhart control chart, so for this also, “ SR=constant”.

Explanation: We know that only Shewhart control chart have the SR value equal to constant. As EWMA chart is not a Shewhart chart, it does not have a constant SR value.

Here, w is called the value of EWMA statistic.

We get the inference that, SR(EWMA)∝1/λ, so SR(EWMA) will be larger for smaller values of λ.

Explanation: To counteract the signal resistance’s higher value in the case of low λ value, we use the Shewhart control charts in conjunction with an EWMA chart.

Explanation: Woodall and Mahmoud (2005) recommended to always use a Shewhart control chart with a EWMA chart (especially when λ is small), as one way to counteract the signal resistance’s high value.

Explanation: We know that Shewhart control charts are used with the EWMA control charts. They provide advantages like easy ARL adjustment, counteraction to high signal resistance value, and detection of larger process shifts, without lowering the ability to find lower process shifts.

Explanation: It is experimentally determined that if the process data does not follow the normal distribution, then the Shewhart control charts ARL value will be quite less than the value expected based on the normality assumption.