Figure 1: The 21 cm line rotation curve of the spiral galaxy NGC 2403 (points with error bars). The dashed curve shows the Newtonian rotation curve of the visible disk, assuming a constant mass-to-light ratio of 0.9 in solar units. The dotted curve is Newtonian rotation curve due to the gaseous component (hydrogen plus primordial helium). The solid curve is the MOND rotation curve. One should bear in mind that such theoretical curves also possess error bars, or a range of confidence, due to observational uncertainties in the baryonic mass distribution.