Scientists have determined that after roughly 500 to 750 days, the difference between Earth rotation time and atomic time would be about one second. The International Earth Rotation and Reference Systems Service (IERS) is the organization which monitors the difference in the two time scales and calls for leap seconds to be inserted in or removed from UTC when necessary to keep them within 0.9 seconds of each other. Since 1972, 26 additional leap seconds have been added at intervals varying from six months to seven years. The most recent was inserted on June 30, 2015. The Coordinated Universal Time (UTC) is computed in Paris, France, at the International Bureau of Weights and Measures.