This is from Wiki Commons, but the data is from IERS (International Earth Rotational Services) that monitors the orientation of the earth with respect to "fixed stars". The red line is the cumulative deviation of the rotation of the earth from a 24 hour day, the red dots are leap seconds, corrections to UTC. The green line is the smoothed measured "excess length of day", the gray line is the unsmoothed measurements of the length of day. The green line is the derivative of the red line. If it stays negative long enough, we will need to subtract leap seconds.