HI-line profiles for three representative ALFALFA sources. For each galaxy the velocity width, W₅₀, is measured between the two outermost points where the flux density falls to 50% of the peak value (red vertical lines). Left panel: MW analog with a typical “double horned” profile, indicative of a mostly flat outer rotation curve. Central panel: dwarf galaxy with a “boxy” profile shape. Right panel: extreme dwarf galaxy with a clearly “single-peaked” profile, suggestive of a rising rotation curve. Keep in mind that narrow profiles can also correspond to intrinsically high-width objects that are oriented close to face-on. Note also that the velocity span of the x-axis in all three panels is the same (1800 km s^-1), and so profile widths are plotted to scale.