For some years the need for these precise measurements has been satisfied by an assortment of various manual alignment equipments. ... The function an alignment system serves is basically to answer the questions: (a) Is it straight ? (b ) Is it flat? (c) Is it square ? (d) Is it level? ... The laser beam a or more properly a the cen- troid of energy of the beam, is a source of a straight line, a real straight line.