Spectral line profile and bisectors of Fe i 6301.5 Å observed in the Quiet Sun at disk center. The line profile is drawn as a black solid line in the left panel, with intensities normalized to the spectral continuum and air wavelength in Å. An exemplary bisector is indicated as a gray horizontal line. All center positions of the bisectors are shown as black asterisks, their interpolation is displayed as a red solid line. In the right panel, the wavelengths were translated into Doppler velocities in m s^-1.