A low offset voltage buffer which comprises a first, second, third and fourth MOS device, each comprising a gate, a source and a drain; a current source coupled to the drains of the first and second MOS devices; a current sink coupled to the sources of the third and fourth MOS devices; an input coupled to the gate of the third MOS device and an output coupled to the source of the first MOS device. A micromirror device under test is mounted on a black box containing a light source such as a laser and a position sensitive device. The resulting product from the semi-solid metal casting method with the vertical indexing casting machine is also provided. The rigid member includes a heat resistant plate rigidly mounted to the walls of the cover which include lower edges and upper edges aligned in a common plane.