more accurate ones following the first series of observations, to allow the monitoring of much weaker sources than previously. Both the source subtractor dishes, and the VSA itself, are surrounded by large metal ground shields. As the VSA is an interferometer, it directly measures the angular power spectrum of the CMB, rather than having to construct a map of the sky first. Results The fields observed with the VSA were chosen to minimize the amount of bright radio sources and large clusters in the field (the latter to avoid the Sunyaev-Zel'dovich effect), as well as to avoid contamination by emission from our galaxy. The radio point sources present in the VSA fields were observed with the Ryle Telescope at 15 GHz, then monitored by the VSA source subtracters during the VSA observations. In the compact array configuration, the telescope observed three 7×7 degree areas of the sky to high precision in an observing session between August 2000 and August 2001. These observations were taken at the highest frequency of the telescope, centered at 34 GHz, to reduce foreground contamination. Another, larger area of the sky was also observed, but less precisely. The data from these observations were reduced independently at all three involved institutions. The results from these observations were published in a series of four papers in 2003; those by Watson et al., Taylor et al., Scott et al. and Rubino-Martin et al. (see References below). The key results were the power spectra of the Cosmic Microwave Background between multipoles of 150 and 900, and the resulting limits on cosmological parameters when combined with data from observations from other experiments. The second observing session ran between September 2001 and July 2003, and was using the extended array. The first results from the extended array were published as a Letter in 2003, simultaneously with the first four publications, using data taken up until April 2002. The sections of the sky observed were located within the previously-observed fields, with the measurements being both more accurate and in greater detail. The result was an improved power spectrum of the CMB, going out to a multipole of 1400, and refined cosmological parameters. The second set of results were published in 2004, and consisted of the original observations plus more observations taken in the same regions of the sky, as well as observations in three new regions. This yielded measurements of the CMB power