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I-MR chart

When n=1, use the I-MR control chart but in that chart sigma calculated used by d2 and when we are select the d2 value as per sample size so why in that case we use d2=1.128 means d2 value of sample size 2.

 

 

 

 

 

Thanks in advance

GraphicsRe: I-MR chart

Because the default number of observations to create each moving range data point is 2, and those 2 observations are successive wrt to the time series sequence.

Re: I-MR chart

Hi Bartell,

Thanks for your reply.

I do agree that 2 data points required for moving range chart, but those two observations or data points belong to same group then how can we consider them as 2 groups & d2 is taken as 1.128 which is applicable for 2 groups. Please give clarity.