Dear Bart, According to your suggestion I wrote to maintainer of the package and the reply which I got is as follows:-
"You shouldn't use R charts for monitoring dispersion using sample sizes larger than 20, and for sample sizes greater than 25 you get an error. From theory, R chart used the distribution of relative range for estimating sigma, which is tabulated up to a sample size of 25 " So R charts should not be used in case the group sample size is greater than 25. -- View this message in context: http://n4.nabble.com/problems-with-SPC-charts-in-R-tp1467901p1478091.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
