An inspector wants to develop 3-sigma level control charts (below table provides factors for 3 sigma level) for the weight of firewood that comes in a bag. Due to uneven shape of wood, weight of bag varies a lot.

Draw X-bar chart and R-chart. For both charts, calculate UCL, CL and LCL by using the factors provided in the table. Is the process in control? Discuss your conclusion.

Weight in pounds from 4 days with sample size of 3 (3 observations each time, n=3) are:

Day 1	Day 2	Day 3	Day 4
23	24	26	28
25	28	28	32
22	24	30	32

Factors for 3 Sigma level

Sample Control Limit Factor Control Limit Factor

Size for Sample Mean for Sample Range

n A2 D3 D4

2 1.880 0 3.267

3 1.023 0 2.575

4 0.729 0 2.282

5 0.577 0 2.116

10 0.308 0.223 1.777