The Haines Lumber Company makes plywood for residential and commercial construction. One of the key quality measures is plywood thickness. Every hour, five pieces of plywood are selected and the thicknesses are measured. The data (in inches) for the first 20 subgroups are in the file Haines.

a. Construct an x̅-chart based on these data. Make sure you plot the centerline and both 3-sigma upper and lower control limits.

b. Construct an R -chart based on these data.

c. Examine both control charts and determine if there are any special causes of variation that require attention in this process.