all sources have typical spectral indices, but we note that in the 16 clusters additionally observed by [@Coble2007], only 1 ‘new’ source, i.e. a source not previously identified in NVSS, was found. However, the quality of our knowledge of the population of sources with mJy flux densities at 30GHz is poor. We were able to run an additional check for ‘new’ sources lying in OCRA–p’s reference arcs. We binned the data by parallactic angle to look for contaminating sources that might produce false SZ effects. Although this subdivides the data, and so leads to a noise level that is higher by a factor of $2 - 3$ than the central measured flux density averaged over all parallactic angles, no previously uncatalogued sources were detected.

X-RAY DATA
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Deriving cluster parameters {#sec:X}
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Our sample has 15 clusters in common with an upcoming X-ray paper, Giles et al. (in prep), some results from which were made available in advance for this work. The remaining two clusters (ZWCL1953 and RXJ1532.9+3021, which lie outside Giles et al.’s specified redshift range of $0.15<z<0.30$) were analysed using an identical method. The authors use *Chandra* ACIS–I and ACIS–S imaging and spectroscopy for each cluster as available 