Chapter 13, Problem 13.92ACI

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 .5 to .85 micrometer wide. A manufacturer of CPU chips knows that if the circuit paths are not .5−.85 micrometer 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 8:00 a.m. until 4:30 p.m.) for 5 consecutive days and measured the circuit path widths. These data were used to construct an $\bar{x}$-chart and R-chart. shown above. What do the charts suggest about the stability of the process used to put circuit paths on the CPU chip? What do the charts suggest about the presence of special causes of variation during the time when the data were collected?