Reid & Sigrist
Turn and Slip Indicator, Mk IA, 6A/675, RAF
Here is a Turn and Slip Indicator, Mark IA, Type 6A/675, invented by George Reid (according to the 'all-knowing' Wikipedia) and made by Reid & Sigrist, as used on the blind flying panel of aircraft of the British Royal Air Force and the Royal Australian Air Force of WWII. It is an early version as evidenced by the all-white markings; later versions had both white and green markings on the face.
The Mark IA was used across numerous British aircraft during the war, including the Spitfire, Hurricane, Beaufighter, Mosquito, Sunderland, Lancaster, Battle, and Anson. This is a unique example because the tamper-evident wire and seal that connects the dial rim with the body is still intact, see photo. The pneumatic filter is also in place and intact. Definitely one of the finest examples we've come across. Measures ~4.25 inches diameter and in depth.