Carlingnose Battery – Control Post and Depression Range Finder

Battery Control Post

Situated to the left of the battery is the Battery Control Post. This was also the observation station for the Submarine Mining Station.
Battery Control Post and Guns
Plan of the Battery Control Post and Battery

The Battery Command Post in 2015.  A Depression Range Finder was mounted on the roof of this building.
( from Fortifications of the Firth of Forth 1880-1977 by Gordon Barclay and Ron Morris.)

Depression Range Finder

Depression range finder – Wikipedia
The Depression Range Finder was invented by Captain H.S.S. Watkin of the Royal Artillery in the 1870s and was adopted in 1881. It could provide both range and bearing information on a target.

A depression position finder measured the range to a target (such as a ship) by solving a right triangle in which the short side was the height of the instrument above mean low water; one angle was the constant right angle between the short side and the plane of the ocean, and the second angle was the depression angle from the horizontal of the instrument as it sighted down from a fire control tower or a base end station at the target.
These calculations were built into the scales and gearing of the instrument as configured for its site, which also corrected for the curvature of the earth and for optical parallax, so the horizontal range to the target could be read from a dial on the DRF.

A Watkins Depression Range Finder

Using A Depression Range-Finder – Fort Pierson, Hobart, Australia

For more information, see the Handbook For Depression Range-Finder for Elevated Batteries