The accompanying table gives sample means and standard deviations, each based on observations of the refractiv index of fiber-optic cable. Construct a control chart, and comment on its appearance. [Hint: and .]
Day s Day s 1 95.47 1.30 13 97.02 1.28 2 97.38 .88 14 95.55 1.14 3 96.85 1.43 15 96.29 1.37 4 96.64 1.59 16 96.80 1.40 5 96.87 1.52 17 96.01 1.58 6 96.52 1.27 18 95.39 .98 7 96.08 1.16 19 96.58 1.21 8 96.48 .79 20 96.43 .75 9 96.63 1.48 21 97.06 1.34 10 96.50 .80 22 98.34 1.60 11 97.22 1.42 23 96.42 1.22 12 96.55 1.65 24 95.99 1.18