A quality engineer monitors the manufacture of liquid detergent and wants to assess whether the process is in control. The engineer measures the pH of 25 consecutive batches of detergent.
The engineer creates an Individuals chart to monitor the detergent process.
One observation, failed Test 1 on the individuals chart (I chart) because the observation is more than 3 standard deviations above the center line. The engineer concludes that the pH level of the detergent is not stable.