This item is a new Melles Griot Shear Plate, a simple interferometer used for checking several laser-related parameters as well as testing some lenses. This device consists of a slightly wedged optical plate that is uncoated and flat to better than lambda/20. The wedge is situated at a 45-degree angle within a cube. On the 90-degree face is a screen with a flat scribed line. The wedge is so situated that a diverging beam will tip the resulting fringes upwards on the right side , a converging beam upwards to the left side. When the fringes are aligned with the scribe line, the beam is collimated to within ~200 microradians. Other uses for the shear plate are the measurement of very long radius mirrors and lenses. The shear plate is initially used to establish a collimated beam, whereupon a lens may then be introduced into the beam path and the rotation of the resultant wavefront measured. With a mirror, the shear plate is reversed so the wavefront is reflected back into the module from the mirror opposite the laser. This particular shear plate is the Model 09 SPM 001, the smallest of the shear plates made, with a clear aperture of 25mm. Minimum beam diameter is recommended to be no less than 5mm (smaller apertures make determination of the fringe tilt much more difficult).