CPU of a computer chip
The central processing unit (CPU) of a microcomputer is a computer chip containing millions of transistors. Connecting the transistors are slender circuit paths only 0.5 to 0.85 micron wide. To understand how narrow these paths are, consider that a micron is a millionth of a meter, and a human hair is 70 microns wide. A manufacturer of CPU chips knows that if the circuit paths are not 0.5 - 0.85 micron wide, a variety of problems will arise in the chips' performance. The manufacturer sampled four CPU chips six times a day (every 90 minutes from 8 am until 4:30 pm) for 5 consecutive days and measured the circuit path widths. These data and MINITAB were used to construct the x-bar chart shown below.
a. Assuming that R = 0.335, calculate the chart's upper and lower control limits, the upper and lower A-B boundaries, and the upper and lower B-C boundaries.
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b. What does the chart suggest about the stability of the process used to put circuit paths on the CPU chip? Justify your answer.
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c. Should the control limits be used to monitor future process output? Explain.