is present in each data cube, which is an order of magnitude lower than the average [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass contained in the candidates ($\mHIcand\sim1.1\times10^8~\ms$, section \[sec:scfinding\]). In the bottom row of Figure \[fig:error\_cleaning\], we perform a similar analysis as in the top row but replace $f_{rel}$ with $N_{rel}$, the number of voxels in the reliable sources. We get similar trends, and the linear relation between $f_{cand}$ and $N_{rel}$ suggests that on average a maximum positive bias in [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass of 0.07$\times10^8\ms$ is associated with the cleaning of reliable sources in a data cube. These tests demonstrate that the cleaning process may indeed leave a small amount of positive residual flux, but it does not significantly affect $\mHIcand$ of the candidates.

Are there faint systematic residuals from continuum subtraction that can not be directly caught by eye? We extract continuum sources from the continuum maps, with a 3 $\sigma$ detection threshold. These sources have a 5 percentile of 0.94 mJy in the flux distribution. We find that 99$\%$ of the flux in candidates comes from sight lines without detectable continuum sources. The fraction is higher than 95% for both positive and negative candidates, if we count them separately. Hence continuum 