Comparison of the HCO⁺ spectra from observations with wobbler switching and position switching modes. The top panel shows the HCO⁺ spectra (velocities relative to the local standard of rest, LSR) taken with WSw (blue) and PSw (red) modes toward G29.96−0.02. The middle panel shows the residual spectrum (green) after fitting the WSw and PSw spectra. Black horizontal dashed lines mark the 3 rms level. The bottom panel presents the combined spectrum (black) of the WSw and rescaled PSw (, where A and B are the slope and y-intercept of a linear least-squares regression fit, respectively), with the individual WSw and PSw spectra in the same colors as in the top panel.