Ecliptic view of the experimental setup (not to scale). Theoretical paths of fast (red) and slow (blue) solar wind packages traced from the spacecraft down to the source surface constitute two coordinate frames. The magnetic polarity is defined by the projection of the magnetic field vector onto the Parker spiral in the respective frame. Two hemispheres are separated by a plane perpendicular to each Parker spiral (colored accordingly). A vector has a positive sign if it lies within the anti-sunward hemisphere (pointing outward, solid half-circle) and has a negative sign if it lies within the sunward hemisphere (pointing inward, dashed half-circle). The depicted hemispheres illustrate the situation in the fast solar wind frame. The slow wind frame has two hemispheres that are defined analogously.