Mariner 10 observations during its first Mercury flyby on the 29 March 1974, inbound (left panels) and outbound (right panels) magnetopause crossings are shown, the associated time intervals are 20:36:30–20:37:30 and 20:53:30–20:54:30, respectively. Magnetosphere (MSP) and magnetosheat (MSH) plasma measurements are shown. From top to bottom, we show the magnetic field module (first row) and its components in MSEQ coordinate (second row) obtained from the magnetometer onboard Mariner 10. Moreover, we show the electron energy spectra as a function of time (third row) and the electron energy spectrum at the time of the crossings (fourth row), obtained from the PLS instrument onboard Mariner 10. The time of the crossings is highlighted by black vertical dashed lines in the first three panels.