Zoom-in on the flux tube: st1. Shown: (A) Magnetic field data in VSO coordinates; (B) The magnetic field in MVA-coordinates; (C) The cone angle θ_c; (D) The clock angle ϕ_c; (E) The electron density determined from RPW (red) and SCP (black); (F) The time-energy spectrogram of the EPD-STEP instrument. The three dotted vertical lines show where B_z changes sign and has its minimum negative value. The horizontal line at 0.01 MeV in panel F is an instrumental artefact.