A method for measuring flatness of a foundation to which a structure, machinery or equipment is to be mounted, comprising the steps of: defining an x-, y- coordinate system; determining x- and y-coordinates within the coordinate system of positions (2, 4, 6, 8) at which mounting points are to be located and storing the coordinates in a reference table in a computer; generating and moving a single laser beam, which generates a point in a plane normal to the direction of propagation, in a horizontal plane in a manner which causes the laser beam to sequentially intercept each of the measurement points; generating signals from a respective position sensor (10, 20) located at each measurement point based on illumination of the sensor by the laser beam; determining coordinates of each of the measurement points from the signals generated by the respective sensor and comparing the determined coordinates to the stored coordinates of the measurement points so as to match a height measurement obtained from a vertical position of impingement of the laser beam on the sensor at each measurement point with a particular measurement point; and determining the actual height (z) of each of the measurement points from height measurements obtained as an indication of the flatness of the foundation, wherein the coordinate determining step comprises using the time difference between when a single laser beam first enters and then leaves a detecting area of the respective position sensor at each of the measurement points in a calculation to determine the distance of each measuring point from the laser based upon the length of the detecting area in said horizontal plane, wherein the step of generating and moving the laser beam includes rotating the laser beam at a constant velocity in the horizontal plane, wherein the step of generating signals includes generating electric pulses, and wherein it is detected when the pulses are coming at a steady rate in order to decide that the sensor has arrived at another measurement position. defining an x-, y- coordinate system; determining x- and y-coordinates within the coordinate system of positions (2, 4, 6, 8) at which mounting points are to be located and storing the coordinates in a reference table in a computer; generating and moving a single laser beam, which generates a point in a plane normal to the direction of propagation, in a horizontal plane in a manner which causes the laser beam to sequentially intercept each of the measurement points; generating signals from a respective position sensor (10, 20) located at each measurement point based on illumination of the sensor by the laser beam; determining coordinates of each of the measurement points from the signals generated by the respective sensor and comparing the determined coordinates to the stored coordinates of the measurement points so as to match a height measurement obtained from a vertical position of impingement of the laser beam on the sensor at each measurement point with a particular measurement point; and determining the actual height (z) of each of the measurement points from height measurements obtained as an indication of the flatness of the foundation, wherein the coordinate determining step comprises using the time difference between when a single laser beam first enters and then leaves a detecting area of the respective position sensor at each of the measurement points in a calculation to determine the distance of each measuring point from the laser based upon the length of the detecting area in said horizontal plane, wherein the step of generating and moving the laser beam includes rotating the laser beam at a constant velocity in the horizontal plane, wherein the step of generating signals includes generating electric pulses, and wherein it is detected when the pulses are coming at a steady rate in order to decide that the sensor has arrived at another measurement position.