Visualisation of how the angle of the arms of the phase spiral is found. Upper row: number density contrast of the two-armed phase spiral at low, medium, and high θ_ϕ. The spiral angle is marked with a red line and the zero-point for the angle is a dashed white line. Lower row: model of the two-armed phase spiral corresponding to the data in the top row. The spiral angle and measurement distance are marked with a red line and a white ring respectively.