GEO600 is a ground-based gravitational-wave detector near Hannover, Germany. It is the product of the GEO Project, a German/British collaboration to detect gravitational waves. It was constructed in the 1990s and first taking data around 2002 and has since undergone improvements. Its basic design is similar to LIGO, a large Michelson interferometer, in GEO's case with 600 meter arms. (LIGO's are 4 km and Virgo's are 3 km, giving them more sensitivity.) GEO600 It has no unequivocal GW detections, but has had value in developing and testing technology and gaining knowledge, which has contributed to LIGO and Virgo.