Observable quantities (Q2 and Q4) in Stokes-V (|V′ |) for a scaling value of α = 10⁻⁴. Panel a: Q2 (high-passed filtered intensities) vs. time. Panel b: Q2 scatter plot for the ON- and OFF-beam. Panel c: Q4a (number of peaks). Panel d: difference of ON–OFF for Q4a. Panel e: Q4b (power of the peaks). Panel f: Q4c (peak asymmetry). Panel g: Q4d (power asymmetry). Panel h: Q4e (peak offset). Panel i: Q4f (power offset). See Sect. 4.3 for a detailed description of each observable. For all plots the black lines are the ON-beam and the red lines are the OFF-beam. The dashed line for panels c and e–i is the mean of the derived Q values from 10 000different Gaussian distributions with the same length as Q2. The dashed lines for panel d are the 1, 2, 3σ statistical limits of the difference between all the Q values derived from two different Gaussian distributions (each run 10 000 times).