Table

Factors for Calculating Three-Sigma Limits for the x-bar Chart and R-Chart

Size of Sample (n)	Factor for UCL and LCL for x-bar-Charts A2	Factor for LCL for R-Charts D3	Factor for UCL for R-Charts D4
2	1.880	0	3.267
3	1.023	0	2.575
4	0.729	0	2.282
5	0.577	0	2.115
6	0.483	0	2.004
7	0.419	0.076	1.924
8	0.373	0.136	1.864
9	0.337	0.184	1.816
10	0.308	0.223	1.777

Source: 1950 ASTM Manual on Quality Control of Materials, copyright American Society for Testing Materials. Reprinted with permission.

Thermostats are subjected to rigorous testing before they are shipped to air conditioning technicians around the world. Results from the last five samples are shown in the table. Create control charts that will fully monitor the process and indicate the result of X-bar and R-chart analysis.

Unit #	Sample 1	Sample 2	Sample 3	Sample 4	Sample 5
1	73.5	70.8	72.2	73.6	71.0
2	71.3	71.0	73.1	72.7	72.2
3	70.0	72.6	71.9	72.4	73.3
4	71.1	70.6	70.3	74.2	73.6
5	70.8	70.7	70.7	73.5	71.1

A bar chart is out of control but r chart is in control

B bar and r chart are both out of control

C bar and r chart are both in control

D bar chart is in control but r chart is out of control