Table 5.1
Factors for Calculating Three-Sigma Limits for the Chart and R-Chart
Source: 1950 ASTM Manual on Quality Control of Materials,copyright American Society for Testing Materials.Reprinted with permission.
-A milling operation has historically produced an average thickness of 0.005 inch with an average range of 0.0015 inch.Currently,the first three items from each batch of 20 are inspected.Use Table 5.1.What is the value of the lower control limit for the x-bar chart?
A)less than or equal to 0.00100
B)greater than 0.00100 but less than or equal to 0.00299
C)greater than 0.00299 but less than or equal to 0.00499
D)greater than 0.00499

Question

Table 5.1
Factors for Calculating Three-Sigma Limits for the  Chart and R-Chart
  Source: 1950 ASTM Manual on Quality Control of Materials,copyright American Society for Testing Materials.Reprinted with permission.
-A milling operation has historically produced an average thickness of 0.005 inch with an average range of 0.0015 inch.Currently,the first three items from each batch of 20 are inspected.Use Table 5.1.What is the value of the lower control limit for the x-bar chart?
A)less than or equal to 0.00100 
B)greater than 0.00100 but less than or equal to 0.00299 
C)greater than 0.00299 but less than or equal to 0.00499 
D)greater than 0.00499

Quizplus · Accepted Answer

- X-bar chart: 
- n=3
- Average range=0.0015
- From Table 5.1, d2=1.693
- Lower control limit= X-double bar-3*Average range/d2
- X-bar = 0.005 (given)
- Lower control limit=0.005-3*0.0015/1.693=0.00499, which falls in the range of "greater than 0.00299 but less than or equal to 0.00499" (Option C)

Table 5.1 Factors for Calculating Three-Sigma Limits for the Chart and Chart