3D configuration schematic interpreting the gyrophase coverage of STEP pixels. The Cartesian coordinate system represents the spacecraft frame. The cyan vector gives the solar wind bulk velocity in the spacecraft frame measured by PAS. The magenta vector indicates the velocity vector of a proton with 4.3 keV energy and 45° PA in the solar wind frame, whose starting point is connected to the end point of the cyan vector. The red vector gives the direction of the magnetic field measured by MAG, whose length equals the value of the magnetic field strength in nT multiplied by 50. The orange spherical surface represents the VDF of 4.3 keV protons in the solar wind frame. Its center is located at the end point of the cyan vector. The torus is composed of the end points of all 4.3 keV, 45° PA (solar wind frame) protons’ velocity vectors, which are color coded according to their gyrophase (color bar on the right). The blue grids and numbers show the FoV of STEP pixels and how the pixels are numbered.