When mirrors exceed 8 meters (26 feet) in diameter, they are no longer rigid enough to maintain the same shape when they are tilted. The Keck I telescope was the first to be built of 36 hexagonal mirrors. The tilt of each mirror is controlled electronically so that they all focus their light rays at a single point. The electronics can position each corner of the mirror to an accuracy 4 nanometers to create the final image. Constructing the telescope of multiple smaller mirrors greatly reduced the cost of the telescope. The Large Binocular Telescope consists of the Keck I and Keck II 10-meter (33-foot) telescopes. When they are used together they can detect the interference of light from a star and thus determine its size and location much more precisely.