There are four different timescales used... civil time, GPS time, atomic time, and they're growing apart: What time is it? Well, no one knows for sure [via 2lmc spool]. Nice image: "Since the debate began, the slowing of the Earth has become less pronounced and no leap seconds should be needed for several years. Experts are unsure exactly why this has happened - a number of factors can have short-term influences on its rotation, including earthquakes and even wind blowing on mountains".