This diffractometer was manufactured for research of solid surfaces and thin
film surfaces and interfaces. To observe the X-rays diffracted from the
surface of a sample in any direction, this instrument has a four-axis
structure comprising 2+2 axes. With an ultra-high vacuum tank that allows
on-the-spot observation, the axes are assembled so that the displacement of
the rotating centers is less than 50??m. The UHV diffractometer has two degrees of freedom (DOF) on the sample and two independent DOF on the detector. The diffractometer is about 3.2 m x 3.2 m x 2.3 m in dimension. This instrument is now in service in the SPring-8 (Super Photon ring-8 GeV) BL13XU in Japan.