When Polaroid reduced the number of quality inspectors and increased operator responsibility for statistical process control in its R2 plant (which made instant film cartridges with 10 films in each) in Waltham, Massachusetts, in 1985, it encountered an unexpected result. Instead of quality improving, it actually got worse. To identify the problem, Bud Rolfs, quality' control manager, asked an operator from each shift to sample six observations of the critical characteristics of the product and report these to him. One important characteristic of instant films is the pod weight. A pod is a small capsule at the end of each film that contains chemicals. When the film is pulled out, the pod bursts and releases the chemicals that will develop tire film. Too much chemical overdevelops the film and too little under-develops it.
a. Use the following three samples of six observations each (in grams) from the first day of the data collection period to develop a sample mean and sample range control chart for the pod weight. Is the process in control?
b. The first sample from the second day is 2.841, 2.802, 2.802, 2.806, 2.807, and 2.807. Is the process still in control?