Abstract: A method for determining from optical measurement a measure of the misalignment, i.e. the deviation in the horizontal plane between the actual and the desired position of a rotatable elongated part (9) of a machine (1). Use is made of an imaginary vertical reference plane (.SIGMA.) lying at a distance from the machine (1). The reference plane (.SIGMA.) is determined by two base points (3, 4) which set up an imaginary base line (.GAMMA.) at an angle (.uparw.) relative to the longitudinal axis (L) of the machine (1), and by an optically reflecting device (5) disposed such that any cross-section thereof with a horizontal plane is a straight line at right angles to the imaginary reference plane (.SIGMA.). With an optical or electro-optical measuring instrument (7) equipped for angle measurement, and a further optically reflecting device (10) being placed on said machine part (9), the angle (.phi.) between the line of sight (Z) of the measuring instrument (7) and an arbitrary imaginary line (.OMEGA.

Abstract: A method for optically aigning a machine part which should have its center line perpendicular to the vertical plane of a reference. The deviation in the horizontal and in the vertical plane between the actual position and the desired position of the part is numerically determined through the use of a theodolite. For determining the deviation in the horizontal plane two reference marks are provided entirely outside the machine at a distance as far as possible from each other. The distance between the two reference marks determines both a base line running parallel to the longitudinal center line of the machine and the position of the vertical plane of reference.