Difference between the velocity perturbation caused by an example radial p-mode (l = 0, n = 20, ω_nl/2π = 2.90 mHz) of amplitude 1.0 m/s (at the surface at the disk center) computed from the HMI algorithm (without background velocity) and a simple line-of-sight approximation evaluated at the formation height at each position on the disk, h_μ, or at disk center, h_μ = 1. We note that δv_los is purely imaginary so that Re[δv_th] and Re[δv_geom] are a deviation from the simple line-of-sight approximation. A center-to-limb effect is observed in the imaginary part and in the thermodynamic contribution. For this radial mode, the geometrical component is small.