Bell's Station Keeper
Bell's Station Keeper, Pattern 494, was an optical device used in the Royal Navy for rough-and-ready estimate of ranges, useful to ensure one's own ship was at the correct distance from another.
It had a prism within which would ship an object 16 feet at 200 yards, or 40 feet at 2.5 cables. Presumably, there were common rules-of-thumb to apply to this angle which would facilitate a quick determination at common distances such as between columns or to the ship ahead.[Inference]
- Handbook of Torpedo Control, 1916. pp. 59-62.
- Admiralty, Gunnery Branch (1917). Handbook of Torpedo Control, 1916. C.B. 302. Copy No. 141 at The National Archives. ADM 186/381.