Estimating process parameters. The 
and s control charts for the meshtensioning example (Figures 27.4(b) (page 27-13) and 27.7 (page 27-19)) were based on µ= 275 mV and σ =43 mV. Table 27.1 (page 27-12) gives the 20 most recent samples from this process.
(a) Estimate the process µ and σ based on these 20 samples.
(b) Your calculations suggest that the process σ may now be less than 43 mV. Explain why the s chart in Figure 27.7 (page 27-19) suggests the same conclusion. (If this pattern continues, we would eventually update the value of used for control limits.)
FIGURE 27.7:
