Reconstructed maps of the large-scale field of GJ 3378 in seasons 2019, 2020, and 2021 (from top to bottom). The left, middle, and right columns represent the radial, azimuthal, and meridional field components in spherical coordinates. The colour bar is expressed in Gauss. The maps are shown in a flattened polar projection down to latitude −60° with the pole at the centre and the equator depicted as a bold line. Outer ticks indicate phases of observations, assuming a rotation period of 95.1 days and counting from an arbitrary BJD of 2458745.0.