If you provide the sample size, estimated standard deviation, and power, Minitab calculates the difference you can detect with the test.

For the cooking oil data, Minitab displays power curves; one for each sample size. The power curve represents every combination of power and difference the test can detect based on sample sizes of 20 and 60. As the sample size increases, and the other assumptions are held constant, the test can detect a smaller difference (1.1 versus 1.9) while maintaining the same level of power at 0.90.

With a sample size of 20, the test will not be able to detect the desired difference of 1.5% at the specified power of 0.90. However, with a sample size of 60, the test will be able to detect a difference smaller (1.1%) than the desired difference of 1.5% at the specified power.