Establishing the process capability

An internal quality control standard with an analyte concentration of 50 mg kg is analysed in a laboratory for 25 consecutive days, the sample size being four on each day. The results are given in Table 4.2, which is in the form of an Excel spreadsheet. Determine the value of R and hence plot control charts for the mean and range of the laboratory analyses. 

Sample Number Sample Values Chart Mean Range 

---