99.7% upper and lower control limits in a control chart

A company is producing cylindrical blocks for a children’s toy. The average diameter of a block is 3.8 inches. A sample of 30 blocks is inspected and the diameters are measured. The standard deviationis estimated to be 0.04 inches.

What are the 99.7% lower and upper control limits for the x-bar chart?.. Answer should be two decimal places

What are the control limits in a control chart? What do they mean? How do we compute them? We go through the mathematical background and an example to demonstrate how to derive control limits. In practice, we also provide an example of using Excel to compute the control limits.