Auto pistons are produced in a forging process, and the average diameter is a critical factor that must be controlled. For samples collected on 5 different days (one sample each day, each sample contains 10 pistons), the mean and the range of the diameters have been measured as follows: Day Mean (mm) Range (mm) 1 154.9 4.4 2 153.2 4.8 3 151.6 4.3 4 153.5 4.8 5 156.6 4.5 Choose the right control chart for controlling the average diameter, and find its upper control limit for the confidence level 99.73%. Note: Enter the value of the upper control limit after rounding to two decimal places. Your Answer: 8.10