Viscosity is a critical characteristic in a chemical process. A viscosity sample is taken every two hours. The following table presents the viscosity data for the last 80 hours of operation.

(a) Assess process control and stability. What is the standard deviation estimate of the in control, stable process?

(b) Prepare a normal probability plot of the data. At α = 0.05, do the data fit a normal distribution?

(c) If the viscosity specification is 15.0 ± 2.5, estimate the process capability.

Using Minitab to solve the problem.

Sample	Viscosity	Sample	Viscosity
1	13.3	21	15.8
2	14.5	22	15.7
3	15.3	23	15.1
4	15.3	24	13.4
5	14.3	25	14
6	14.8	26	14.8
7	15.2	27	14.3
8	13.5	28	14.3
9	14.6	29	16.2
10	13.9	30	16.7
11	14.3	31	14.2
12	16.1	32	16.9
13	13.1	33	14.9
14	15.5	34	15.2
15	12.6	35	14.4
16	14.6	36	15.2
17	14.3	37	14.6
18	15.4	38	16.4
19	15.2	39	14.2
20	16.5	40	15.7