(A, A’) To quantify bi- and uni- directional polarisation of Myosin II, we aim at identifying either two peaks (A) or one peak (A’) around the perimeter of a given cell. Myosin II fluorescence intensities (f.i., y-axis) are plotted along the unwrapped cell perimeter from 0 to 360 degrees (x-axis), starting from the East side of the cell and going anti-clockwise. (B-D’) We used two different methods, 'Fourier' and 'Gaussian', to identify one (unidirectional polarity) or two (bidirectional polarity) peaks in the Myosin II fluorescence signal around the perimeter of each cell. Graphs B-D’ show simulated data for a cell with either bidirectional polarity in Myosin II (B,B’) or unidirectional polarity (C,C’) or a mixture of the two (D,D’). In the first method (B, C, D), Fourier decomposition gave period 1 (unidirectional polarity) and period 2 (bidirectional polarity) amplitude estimates. In the second method (B’, C’, D’), two Gaussians curves with their means 180 degrees apart were fitted to Myosin II fluorescence intensities through minimisation, varying the amplitude of each Gaussian curve and a standard deviation common to both. (B, B’) Example cell with bidirectional polarity. Both Fourier (B) and Gaussian (B’) methods succeed well at fitting the two peaks of Myosin II intensities (fluorescence intensities, f. i., represented as a black castellated curve as in A,A’). (C, C’) Example cell with unidirectional polarity. The Fourier method fits a unidirectional peak at the correct position, but because the Myosin II signal is discrete, or castellated, there is also a strong period 2 harmonic in phase with the unidirectional signal. Thus with the Fourier method, the quantification of uni- and bi- directional polarities is not completely independent: specifically the period 2 estimate used for estimating bidirectional polarity will also describe some of the unidirectional polarity signal (C). Gaussian fitting finds the correct unidirectional peak (C’). (D, D’) Example cell with a combination of uni- and bidirectional polarity. Similar to (C), the period 2 amplitude is augmented by the castellated signal in the Fourier method (D), whereas the Gaussian fitting correctly identifies two independent peaks of different amplitude: the smallest amplitude identified by the West peak (blue) corresponds to the bidirectional polarity, whereas the higher East peak correspond to the unidirectional polarity (D’).