Question

Q-1 Every hour a quality control inspector measures the outside diameter of four parts. The results of the measurements are shown below.

Sample piece and Time

Time

1

2

3

4

9 A.M

1

4

5

2

10 A.M

2

3

2

1

11 A.M

1

7

3

5

(a) Compute the mean outside diameter, the mean range, and determine the control limits for the mean and the range. (b) Are the measurements within the control limits? Interpret the chart.

Q-2 Describe the difference between assignable variation and chance variation.

Q-3 Describe the difference between an attribute control chart and a variable control chart.

Answer 1

Q1.

Q2.

Chance variation is random in nature and because the cause is a variety of factors it can-
not be entirely eliminated.

Assignable variation is not random, it is usually due to a specific cause and can be eliminated.

Q3.

Variable control charts are concerned with
actual measurements (weight, diameter, etc.).
Attribute control charts are based on a
classification of acceptable or not acceptable
(door lock either works or it does not).