Purpose: Apply statistical process control, including the visualization graphs.

Task: Use Excel to compute the control limits$,$ and also graph the observations and show the

centerline and control limits for both Xbar and R charts. Plot the observed data points using a

scatter diagram, and then add lines for each control limit and the centerline $($a picture is worth a

thousand words! $-$ and this is what you would call data visualization$).$

Context: $\frac{x}{b}ar\frac{?}{R}$ charts are used in conjunction to give the user a fuller understanding of sampled

output, to determine not only if the overall sample averages or means are within control, but also

whether or not the Range is in control. Consider a sample size of six, when you are striving for a

target of $3($could be $3$ minutes to complete a phone call with a customer, or $3$ inches, as in the

diameter of a baseball$).$ If you measured $1,1,1,5,5,5$ for your observations within the sample, the

mean would be $3(\frac{18}{6})$ which is perfect $-$ but not really, as there wasn't one observation anywhere

close to a $3.$ That's why we also need to consider the Range, along with the mean. The Range is

fairly wide for this sample, at $4-$ and it would certainly not be in statistical control.