a dispersive element introduced in the optical path of the test beam such a compensation element may consist of a single optical component or of multiple components optically coupled to produce a desired effect the term u201c dispersive element u201d is used to refer to any transparent substance or cover on a sample surface in the optical path of a test beam of a profiler used to measure the surface such dispersive elements may also be referred to as transmissive plates in the description of the invention the term u201c plate u201d is intended to encompass any shape of such dispersive elements whether or not it approximates the actual geometry of a plate and can include compound elements such as a fluid cell containing a liquid sandwiched between two layers of glass or plastic the term u201c half cube u201d is used to refer to a prism having the geometry of a half cube that results from splitting a cube along a diagonal plane in addition any parallelepiped or other prism capable of producing the effects of the half cubes described herein is similarly referred to as a half cube for the purposes of the invention referring to the figures wherein like parts are referenced with the.