Say you have a process in which the center line is 100, and the LCL and UCL are 90 and 110 respectively.

These have been computed using z=3, or 99.73% confidence intervals.

If you change to z=2.58, to a 99% confidence interval, you would expect

1. The limits to become wider - the LCL will go down and the UCL will go up
2. The limits to become narrower - the LCL will go up and the UCL will go down
3. The limits to remain unchanged
4. A point which was out of control at z=3 will become in control at z=2.58