Found this on a coastal defence site. Markings suggest it fitted a Mk VII 6 inch gun. I am interested to know exactly how these discs were fitted and connected to the sight mechanism. Can anyone help with technical or diagrammatic details. I suspect from the little info I could find on them that they had a short use life as when new shells were developed a new disc with appropriate calibrations had to be fitted to the gun.

Cheers

IMG_0520.jpgIMG_0517.jpgIMG_0519.jpgIMG_0518.jpg