Time–distance ΔI map constructed along the slit FIL. Each cyan-colored dashed line segment traces the trajectory of a filament at each instant, and its slope corresponds to the instantaneous velocity at one particular instant, as explicitly specified by a cyan-colored number (in units of km s⁻¹). Each red sinusoidal curve traces the transverse oscillation of the filament, which is indexed by red numbers ranging from 1 to 4.