Virgin Media's political correspondent Gavan Reilly sits down with us to explain what exactly proportional representation with a single transferable vote is all about. Do you need to give a preference to every candidate listed on a ballot paper? How and when do preferences beyond your first come into play?The Explainer is brought to you by The Journal. Providing open access to valuable journalism in Ireland has been the aim of The Journal for a decade. You can contribute to ensure we can keep questioning, investigating, debunking, explaining and informing at www.thejournal.ie/contribute/