Consider the data in Exercise 15-9. Calculate the sample standard deviation of all 60 measurements and compare this result to the estimate of σ obtained from your revised X̅ and R charts. Explain any differences.

Exercise 15-9

The pull strength of a wire-bonded lead for an integrated circuit is monitored. The following table provides data for 20 samples each of size 3.

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Sample Number 15,3 15.4 15.6 15.4 17.1 15.2 3 16.1 16.1 13.5 4. 13.5 12.5 10.2 17.0 5 18.3 16.1 17.2 19.2 19.4 14.1 12.4 11.7 15.6 13.3 13.6 15.5 13.9 14.9 18.7 21.2 10 20.1 11 15.3 13.1 13.7 18.0 12 16.6 18.0 13 17.0 15.2 18.1 14 16.3 16.5 17.7 7.7 15 8.4 8.4 16 11.1 13.8 11.9 17 16.5 17.1 18.5 18 18.0 14.1 15.9 17.8 19 17.3 12.0 20 11.5 10.8 11.2