The viscosity of a chemical intermediate is measured every hour. Twenty samples consisting of a single observation are as follows.
(a) Using all the data, compute trial control limits for individual observations and moving-range n = 2 charts. Determine whether the process is in statistical control. If not, assume that assignable causes can be found to eliminate these samples and revise the control limits.
(b) Estimate the process mean and standard deviation for the in-control process.