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    $\begingroup$ Ummm... what's the "SG" method? $\endgroup$ Commented Aug 29, 2023 at 5:00
  • $\begingroup$ A result of x=29.4461 seems o.k. considering the noise. $\endgroup$ Commented Aug 29, 2023 at 10:05
  • $\begingroup$ I'm confused. The plots show such a big range that the presumed knee at around x=29 isn't visible. If you expect it to be there, why not restrict the data range up to, e.g., x=50? $\endgroup$ Commented Aug 29, 2023 at 10:54
  • $\begingroup$ I faced a similar problem when computing the knee of viscoelastic curves. I managed to implement a robust method in the WL. The basic steps were: (1) Rescale the curve so that $x$ and $y$ are in $[0,1]$. (2) Rotate the coordinate system counterclockwise by 45 deg and calculate the rescaled coordinates of the points. (3) Calculate the 1st derivative using the SavitzkyGolayMatrix. (4) The zero point of the 1st derivative determines the knee. In my opinion, the position of the knee is a matter of consensus; it is important that the method produces consistent and robust results. $\endgroup$ Commented May 2 at 16:56