Use the power curve to help you choose the appropriate sample size or power for your test. This power curve plots the power of the test versus the difference. Difference refers to the difference between the null hypothesis and the reference value that you choose for the Z-test.

If you provide the difference that you want to be able to detect and the size of your sample, Minitab will calculate the power of the test.

For the cooking oil data, the power curve represents every combination of power and difference for the test based on a sample of size 13, alpha of 0.05, and a standard deviation of 2.6. The symbol on the power curve represents the calculated power of 0.547849 for test that can detect a difference of 1.5%.