At midnight on June 30th an extra second will be added to the worldwide clock. While this SHOULD be unnoticeable and is considered low risk, you may: Wonder why you are 1 second early to everything Wonder what caused unexplained schedule/event issues or weird crashes or system behaviors. Wonder why you feel so rested In the past, leap seconds have caused problems for computer systems, often because scientists don’t know about the extra second until the last minute (figuratively speaking). Leap second addition last occurred on June 30, 2012 and caused issues for Reddit, LinkedIn, Gizmodo and FourSquare (The Inside Story of the Extra Second That Crashed the Web, WIRED)….