I'm in a situation where I'm provided with a signal and a couple of measurement values for that signal. Usually the signal will drift a little when the measurement start (i.e. because of heat). I want to determine whether my system is still drifting (at any given point) or not. Therefore I wanted to determine a regression line and used the equations for linear regressions (https://en.wikipedia.org/wiki/Simple_linear_regression), but the result is awkward and cannot be correct. So the question is, what am I missing?