Visualization of the busy function fit to determine the systemic velocity of IC 1553. The integrated Hα profile was obtained by collapsing the data cube along both spatial axes for bins with altitude |z|≤10″. The central wavelength of the profile is taken as the mean of the centroid wavelengths of the red- and blue-shifted components in the busy function fit. We estimate the uncertainty in this determination as ±0.5 channel width.