Longitudinal-vertical slice through the standard penumbral filament along the central axis. The line-of-sight velocity is saturated at ± 2.5  km s^-1 in order to show weaker flows as well. The arrows in the γ map indicate the direction of the magnetic field, mainly to guide the eye. However, one must keep in mind that, among other things, the optical depth corrugation effect is not taken into account. Thus the geometrical height need not be the same at the head and tail of the filament.