The accuracy of our redshifts, compared to values from the literature. All available spectroscopy is included, not only Hα candidates. Bottom: our redshifts match well with those from the literature. Of note is the high density of sources around the cluster redshifts, whose distribution is shown in the histogram. Top: the distribution of shifts between the literature redshifts and our redshifts (note the logarithmic scale). The bulk of the sources have matching redshifts within 0.0005.