Statistics Toolbox

S Charts

The S chart is a plot of the standard deviation of a process taken at regular intervals. The standard deviation is a measure of the variability of a process. So, the plot indicates whether there is any systematic change in the process variability. Continuing with the piston manufacturing example, we can look at the standard deviation of each set of four measurements of runout.

• schart(runout)
  
  
  

The average runout is about 0.1 thousandths of an inch. There is no indication of nonrandom variability.

Xbar Charts

EWMA Charts