Self-referenced prism deflection measurement schemes with microradian   precision
  We have demonstrated several inexpensive methods which can be used to measure the deflection angles of prisms with microradian precision. The methods are self-referenced, using various reversals to achieve absolute measurements without the need of a reference prism or any expensive precision components other than the prisms under test. These techniques are based on laser interferometry and have been used in our lab to characterize parallel-plate beamsplitters, penta prisms, right angle prisms, and corner cube reflectors using only components typically available in an optics lab. 
Rebecca Olson, Justin Paul, Scott Bergeson, Dallin S. Durfee