File:Radiogoniometer RN S25 assembled.jpg

English: The Royal Navy S 25 radiogoniometer assembled in operational condition. The working mechanism can be removed from the box for maintenance, and can be seen in this condition in another image. The S 25 was an advanced form of the Bellini-Tosi radiogoniometer concept. In general one would use the knob while listening to the signal via headphones connected to the terminals on the right. The S 25 added two more pointers which could be used to record the outer fringes of the signal, as signals rarely worked "perfectly" and reached a maximum or a null at a specific point. The right-hand pointer could be moved and then locked into position with the small arm seen in the image (although the precise operation of this is not clear). The left-hand arm was then moved using the small knob at the pointer end. Moving these arms caused the center arm to move to the average position of the two.