30GHz is generally low for bright clusters, producing only small corrections to the SZ data, and thus introduces little bias as a result of the limitations of the method employed. Although we are confident that residual biases are below the level of our errors, we recognise that the absence of 30GHz data is a limitation in some cases, and there may be additional issues to do with source variability. For clusters where radio sources fall in the OCRA reference beams, we are able to perform an additional check by flagging out contaminated data based on the range of parallactic angles affected by the source in question. We compare the flagged data with the corrected data, and adjust our final measurement error accordingly.

We recognise that our strategy may miss sources which are important at 30GHz. The flux limit of NVSS is $\sim2.5$mJy. If we consider a source of flux density $\sim2.4$mJy at 1.4GHz, and assume a typical spectral index of $-0.7$, extrapolating to 30GHz gives a flux density of $0.34$mJy. Even if such a source were to be located in the central regions of a cluster, the effect on our measurement would still be small relative to random errors. Not 