the Stokes Q cubes is indeed close to 0.

In addition, we visually inspect the data cubes carefully in various projections. The well trained eye is able to spot and identify systematics in the data. Because the WSRT is a linear E-W array, bright RFI residuals show patterns of parallel stripes and bright cleaning residuals show patterns of elliptical rings around bright sources on the Ra-Dec projections. Improper continuum subtraction results in negative regions on the Ra-velocity or Dec-velocity projections (see Figure \[fig:projection\]). We find no obvious cleaning or continuum subtraction residuals. We find some very weak underlying RFI patterns in a few channels, but none of our [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}candidates are associated with any of those. This is partly because the source finder takes into account noise variations within cubes (including those caused by residual RFI; section \[sec:scfinding\])

We continue our search for possible sources of systematic error in our measurement of $\mHIcand$ by investigating the effect of incorrect cleaning and continuum subtraction. Any systematics related to clean residuals [**(i.e. the presence of residual side lobe flux in the HI cubes)**]{} should correlate with a higher cleaned flux or a larger cleaned region. This opens the possibility for the 