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I cannot really understand the real usage of those types of standard deviation and the information that i get in the qcc manual is sometimes confused. I used the example provided in the qcc manual but i don't know for which one i choose and what is the reason for that choice.

I thank a lot for any support.

`# Water content of antifreeze data (Wetherill and Brown, 1991, p. 120)
x <- c(2.23, 2.53, 2.62, 2.63, 2.58, 2.44, 2.49, 2.34, 2.95, 2.54, 2.60, 2.45,
       2.17, 2.58, 2.57, 2.44, 2.38, 2.23, 2.23, 2.54, 2.66, 2.84, 2.81, 2.39,
       2.56, 2.70, 3.00, 2.81, 2.77, 2.89, 2.54, 2.98, 2.35, 2.53)
# the Shewhart control chart for one-at-time data
# 1) using MR (default)
qcc(x, type="xbar.one", data.name="Water content (in ppm) of batches of antifreeze")
# 2) using SD
qcc(x, type="xbar.one", std.dev = "SD", data.name="Water content (in ppm) of batches of antifreeze")`
Phil
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Duban Castillo Cárdenas
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  • Does this [link](https://www.itl.nist.gov/div898/handbook/pmc/section3/pmc321.htm) explain it for you? In short: use a range chart if the sample size is small. (n < 10). – Paul van Oppen Jun 18 '20 at 07:13
  • That information i've found in Douglas Montgomery "Introduction to statistical quality control". The problem is that R use those odd types of standard deviation and i really don't know how it works and exactly how do i choose one by another. Thanks for your support. – Duban Castillo Cárdenas Jun 18 '20 at 21:53

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