You got me there

I study mathematics, and I have a course in statistics and time series analysis behind me.

It is not possible to quantify the uncertainty, it have to be measured or know. Yes, you measure the uncertainty with equipment that you know is more precise than the one you want to know the uncertainty for

As for this test with power measurement, I don't how how they where measured or with what equipment, but without that information the test is useless, and it doesn't tell anything.

If this is not possible, as it sometimes is, you have to do more than 28 measurements for each point. Why 28, because then you are in the 95% confidence interval.

Which means that there is a 95% change that what you have measured is the right values.

100% is impossible. That formula doesn't allow this.

The Phononix test suite is worth nothing (sorry to say so) to anyone with an engineering background. The results doesn't tell a damn thing.