The use of an optical rhomb about 20 m long, consisting of two prisms at the ends of a tube, entails bending and twisting it, and this can cause errors of up to 10′. The theory of an undeformed rhomb subjected to bending and twisting is developed, and the possibility of internally aligning the rhomb to within about 3″ by the methods of geometrical optics is evaluated.
V. I. Mitin, "Theory and practice of using a long-base rhomb," J. Opt. Technol. 73, 854-858 (2006)