The journals included are Eighteenth-Century Studies, Eighteenth-Century Fiction, Novel, Studies in Romanticism, Keats-Shelley Journal, Eighteenth-Century Life, and Eighteenth-Century: Theory and Interpretation. The dates are roughly between 1973-2011, but the coverage varies per journal. In general, there are far more citations from recent issues of the journals. Please see my explanatory post for more detail. The slider controls the number of total citations; the lower the number, the more nodes will appear on the graph.
Please wait until the graph stops moving before adjusting the threshold or dragging the nodes. Chrome and Safari will give much better performance than Firefox, and I doubt this will render well on most phones.