Many of these Night marching compasses were privately purcased by British officers in WW1.
A big radio-active arrow is painted on the north. Radioluminescent paint was invented in 1908 and originally incorporated radium-226. The toxicity of radium was not initially understood, and radium-based paint saw widespread use in, for example, compasses, watches and aircraft instruments. During the 1920s and 1930s, the harmful effects of this paint became increasingly clear.
Contains Radium paint. (1.1 micro sievert/h)