1. A method for measuring the position of a circular object, such as the end or end shield of a paper or board reel, using a measuring device comprising: arranging positions of the measuring device and the circular object to be such that the object is in a detection area of the measuring device; moving the detector along such a circular path that intersects the curve of the circle described by the edge of the object; measuring with the measuring device an angular position of the detector using the curve of the circle over which the detector travels; detecting intersection points of the curve travelled by the detector and the edge of the object; determining a location of the centre point of the object on the basis of: a) the radius of the circular path travelled by the detector, and the location of the centre point of the circular path, b) the location of the tool point of a grab device for grasping the object, c) the assumed radius of the object, and d) the locations of the detected intersection points, determining the position of the centre point of the object in the set of coordinates of the grab device.