Abstract: A method of comparing circumferential shapes, particularly the outer circumference of a desired clearance wth the real clearance between obstacles arranged alongside a railway track, for example, signalling posts, overhead structures and quay walls, wherein from a point on the railway track, with the aid of field-glasses, in the viewing field of which is arranged an image of the outer circumference of the desired clearance made from a given distance, the real clearance is observed in the direction of length of the track at said given distance.