'Harmonic' part of the analysis. The orbital period is determined (if not given), and the orbital harmonics found in the extracted list of frequencies are coupled to the orbital frequency, after which another non-linear optimisation is done. This step is broadly applicable to EBs and other light curves of periodic, non-sinusoidal signal that results in a series of harmonics in the periodogram. The second to last panel shows the orbital harmonic sinusoid model in orange and the bottom panel shows all non-harmonic sinusoids.