Abstract: For the measurement of a large object, a reference point known in the coordinate system of the measuring arm is located by using an optical locating system, when the measuring arm is in the first location. The sensors of the sensor-equipped measuring arm indicate how the measuring tip moves between the different positions of the measuring arm. The sensor-equipped measuring arm is transferred to a second location, in which a new reference point is located. Also in the second location, the sensors indicate how the measuring tip moves between the different positions of the measuring arm. The information indicating the location of the points to be measured is transformed to a common coordinate system by using the information on the location of the first and second reference point and information indicating the location of the measuring tip in each position of the measuring arm.