Physicists in Germany have built a new kind of interferometer that could measure distances up to five hundred times more accurately than existing devices. Many rays of light interfere in the device to create a finely spaced diffraction pattern, which could reveal changes in distance a thousand times smaller than the wavelength of the light used. Yuri Ovchinnikov and Tilman Pfau of the University of Stuttgart believe that their interferometer could be used to make ultra-precise measurements and new optical switches for fibre-optic systems (Y Ovchinnikov and Tilman Pfau 2001 Phys. Rev. Lett. 87 123901).