In order that an accurate subtraction of the continuum from the line emission can be achieved, the user will have to plan ahead and ensure that a sufficient number of channels without line emission are available, situated at either end of the line profile. In that case there are several ways to interpolate across the band and subtract the continuum, such as IMLIN and UVLIN (see the AIPS Cookbook). Some projects benefit tremendously from the latter option such as a weak line in the presence of strong and/or extended continuum emission. In those cases, and for all projects which demand a high spectral line dynamic range, one should avoid using correlator modes which employ two adjacent, partially overlapping IF pairs, as within each IF one will in general find line-free channels on one side of the line profile only. This is of no real concern in situations where the requirements for the spectral line dynamic range are modest, as one can derive the continuum per IF and subtract it from that IF, either in the uv- or map-plane.