Control limits for air conditioner thermostats. A maker of auto air conditioners checks a sample of 5 thermostatic controls from each hour's production. The thermostats are set at 72°F and then placed in a chamber where the temperature is raised gradually. The temperature at which the thermostat turns on the air conditioner is recorded. The process mean should be μ = 72°. Past experience indicates that the response temperature of properly adjusted thermostats varies with σ = 0.4°F.
(a) The mean response temperature x‾ for each hour's sample is plotted on an x‾ control chart. Calculate the center line and control limits for this chart.
(b) The sample standard deviation s for each hour's sample is plotted on an s control chart. What are the center line and control limits for this chart?