Laser MegaJoule and other large optical systems require the metrology of large components. MegaJoule's tilted amplifying slabs, for example, have a diagonal size of approximately 800 millimeters, thus requiring a large interferometer. Large interferometers, 600 millimeters diameter and above, are expensive. This is due, in part, to the large collimator and reference plate required. These parts, being large and heavy, also generate mechanical stability problems. Stitching interferometry is a method by which large optical components are analyzed using a standard 'small' interferometer. This result is obtained by taking multiple overlapping images of the large component, and stitching these 'subapertures' together. Previous papers have dealt with the subject.