the longest baselines, where the SZ signal will be negligible. The uncertainties on the @Coble2007 flux densities are generally a few tenths of a mJy, so given the proximity of the two observing frequencies, we are able to place tighter constraints on our 30GHz source flux densities by fitting to both datasets, which is particularly useful for sources with poor GBT data. In addition, we are able to identify variable sources and estimate the effect on our SZ measurements.

Most source flux densities are well constrained by a combination of GBT and OVRO/BIMA data. We fit a power law to the measurements in the four GBT frequency sub-bands, plus the interferometer data at 28.5GHz. For sources with good GBT data, the @Coble2007 points serve as a valuable check for variability, but otherwise have minimal effect. In the three cases where significant variability is found, we take the two differing flux density measurements, and use half the difference as an estimate of the uncertainty in our measurement due to variability. We then add this in quadrature to the measurement error. The source exhibiting the greatest variability, source 1 in Abell 2261, has little effect on our results since it lies well 