GI2T (Grand Interferometre a 2 Telescopes) interferometer, at the Cote d'Azur Observatory (OCA), on the Calern plateau, near Caussols, France. This instrument, built in the 1970s, is an optical interferometer, combining the observations made by two telescopes to obtain results equivalent to using a much larger telescope. Here, the two 1.5-metre telescopes are around 12 metres apart, but this distance can be adjusted by moving the telescopes on their tracks (lower right). Various beam combining systems (such as REGAIN) have been used with the GI2T system, which closed in 2006.