The basic limitation upon the ability to fabricate a particular surface lies in the ability to accurately test it. Aspheric elements have always presented problems in this regard due to a general lack of test equipment with which to perform the qualification. Lateral shearing interferometry provides a solution for testing a large range of aspheric surfaces since this technique has the ability to decrease the sensitivity to wavefront aberrations. Data reduction can then be used to reconstruct the original wavefront. This Paper examines a data reduction approach and provides the mathematics required to complete the analysis. Also included are the results of a study evaluating the program's performance in the Presence of data input errors.