Figure 6
The first chart is an individual value chart with data points fluctuating around a center line at 11.06. The upper control limit is at 27.18, and the lower control limit is at -5.05. Red squares indicate points where the service process went out of control. The second chart is a moving range chart with data points fluctuating around a center line at 6.06. The upper control limit is at 19.80, and the lower control limit is at 0. Red squares also indicate out-of-control points in this chart. All values are approximated.Control charts for the total service time before the improvement. Source: Authors' own creation