Scientists at DESY have set up the world’s most precise ‘metronome’ for a kilometre-wide network. The timing system synchronizes a 4.7-kilometer-long laser-microwave network with 950 attoseconds precision. An attosecond is a quintillionth of a second, or a millionth of a millionth of a millionth of a second. Such installations can provide the beat for recording ultrafast X-ray snapshots of dynamic processes in the world of molecules and atoms. The German-US team around leading DESY scientist Prof. Franz X. Kärtner from the Center for Free-Electron Laser Science (CFEL) in Hamburg reports the achievement in the scientific journal Light: Science & Applications.