Observed rotation curves. Top: radius in kpc and amplitude in km s^-1. Bottom: radius scaled by h_R and amplitude scaled by the rotational velocity of the flat part of the rotation curve (V_flat). Galaxies with B/D > 0.1 have their first velocity measurement marked by a filled circle. In both panels, black and gray lines indicate high and low surface brightness, respectively. The thick, dashed line in the bottom panel indicates the rotation curve of a thin exponential disk with V_max = 0.85V_c. R = 2.2h_R is indicated with a vertical dashed line.