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Hello everyone, Control limits for R charts are formed using UCL= D4 Rbar LCL= D3 Rbar Where D4 and D3 are values read from tables (for a specific sample size). Could anyone give me a reference where I might find tabulated values for D3 and D4 for really large sample sizes (i.e. n from 100 to around 5000 and possibly beyond!). The largest sample size I can find tables for is 100. Similarly for Xbar charts, if I wanted to calculate sigma_x using Rbar/d2.....are there tables which provide values for d2 for really large sample sizes? The nature of my problem means that it is not possible to reduce the sample size. [In, for example, Minitab we cannot construct control charts when n>100]. Kind Regards, Kim