A dimension of a rheostat knob was specified to be 0.140 ± 0.003 inches. Otherwise the knob would not fit into another part. Five knobs from each each hour’s production were inspected and the dimension was recorded (in units of 0.001 inches) in the following . The sample means and sample ranges are recorded in the last two columns. (a) Draw the histogram of the raw data using the class marks: 132, 134, 136, 138, 140, 142, 144, 146, 148. How many rheostats are non-conforming? (b) Is the process in statistical control? Draw the x and R charts to find out.
(Source: E.L. Grant and R.S. Leavenworth (1996), Statistical Quality Control, 7th ed., McGraw-Hill. Used with permission.)
