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7-72.
  1. 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 ✎

  2. 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

    1. Create an x‑bar process control chart with a UCL of 45 and an LCL of 35.

    2. 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.