Ammunition Rounds Counter, Mk II RAF (NOS)
This interesting device is an Ammunition Rounds Counter for inboard and outboard 20mm guns on an aircraft of the British Royal Air Force. Made in 1942, the device would be set upon ammunition loading, to the rounds per inboard gun and rounds per outboard gun. Given that it says Inboard and Outboard guns, it may have been for a 4-canon aircraft such as the Spitfire or Tempest.
It is new old stock in its original package.