# Quality Control Charts

1. Aug 28, 2011

### Apple&Orange

Hi all
I'm having a bit of trouble trying to calculate the Upper and Lower Control Limit on R chart.

The file "QualityIndex1180" contains the information from which I'm doing my calculations. Ob1, Ob2, and Ob3 are basically 3 samples that have been taken the first of 15 batches on some production process.

Using R, I calculated the grand mean, xbarbar, to be 733/45. Using that, I calculated the Upper Limit to be 16.87 from the formula UCL=Xbarbar-A2*Rbar, where Rbar is 197/75 and A2 is 0.223.
However, using the qcc package on R, and on Minitab, it shows the Upper limit is 18.976

I'm confused to as why its 18.976 instead of 16.87

Cheers
Apple&Orange

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