### Home > INT3 > Chapter 7 > Lesson 7.2.2 > Problem 7-72

A glass factory makes a continuous ribbon of glass by pouring a continuous stream of hot, liquid silicon on a lake of molten tin. The liquid silicon spreads out evenly on the tin and then cools into glass. It is a process that must continue uninterrupted 24 hours a day, so adjustments to equipment and materials are ongoing. Assume that inspectors work eight-hour shifts, watching the glass ribbon as it flows from the lake of tin, marking and counting the number of defects on the new glass. The number of defects identified by the inspectors for one 24-hour period is shown below. Homework Help ✎

Hour

1

2

3

4

5

6

7

8

9

10

11

12

Defects

43

40

42

40

38

39

36

38

44

41

45

42

Hour

13

14

15

16

17

18

19

20

21

22

23

24

Defects

40

37

39

39

43

40

42

42

38

41

38

37

Create an

*x*‑bar process control chart with a UCL of 45 and an LCL of 35.What do you notice about the process control chart that might concern you as a quality control engineer?

Make a graph where the *x*-axis is Hours, the *y*-axis is Defects.

The *y*-axis should range from 35 to 45.

Answers will vary, but notice that there appears to be a cycle every 8 hours.