Abstract: In a method for measuring the flatness of a floor with an inclinometer, the relative elevation of the floor is determined at the beginning and end of a survey line, and then a plurality of inclinometer measurements in one direction along the survey line are performed. The difference in relative elevation at the beginning of the survey line and the end of the survey line is then used so as to correct for accumulated offset errors in the inclinometer measurements. The use of such elevation differences to correct the accumulated offset errors in the inclinometer measurements eliminates the need to perform inclinometer measurements in a reverse direction, and thereby reduces time required for the performance of such measurements. The accuracy of the device is improved by reducing the distance between measurements and by averaging a plurality of consecutive measurements.