Velocity centroid as a function of position along each of the L1517 filaments. Blue squares represent C¹⁸O(1–0) and red triangles N₂H⁺(1–0) values. The spatial scale for filament 3 has been shrunk by a factor of 1.5 in order to fit it into the reduced box size used for the other filaments. The mean formal error in the velocity centroid determination is 0.02 km s^-1 for C¹⁸O and 0.01 km s^-1 for N₂H⁺, which is always smaller than the marker size.