Locate this rangefinder on a wooden mount.
A rangefinder is used to calculate distances. On a warship this might be to calculate where to point the guns to ensure the missiles hit their targets, especially over long distances.
The label of this rangefinder says: 'FA Register no. 174. Dispatched to HM Dockyard in 1898'.
Type FA means it is the same design as the first rangefinder ordered by the Admiralty.