Physicists have used an atomic interferometer to measure the acceleration of individual atoms under the force of gravity to an accuracy of three parts in a billion. This is a million times more precise than previous measurements of g with atomic interferometers, and is nearly as good as the accuracy of two parts in a billion that is possible with the best gravimeters. Steven Chu, Keng Yeow Chung and Achim Peters from Stanford University in the US used an atomic 'fountain' of laser-cooled caesium atoms to make the measurement (Nature 400 849).