Altimeter, 35,000 FT, British RAF
This Altimeter, made by the British aircraft instrument manufacturer Smiths, indicates aircraft altitude up to 35,000 ft. The pointer indicates altitude from 0-20,000 ft with one 360 degree rotation, using the scale along the outer perimeter. Once past 20,000 ft, the pointer indicates altitude along the inner green scale, up to 35,000 ft. With only one pointer and markings every 2,000 ft, this would be regarded as a 'non-sensitive' altimeter.
The center knob adjusts for barometric pressure, which, when rotated, shifts the index line in the small round window at ~19,000 ft to align with the line markings outside of the window.
The fields on the data label do not contain data, so the exact information regarding this indicator are unknown. Based upon information from websites specializing in RAF equipment, this appears very similar to the MkXVII type, 6A/1538 altimeter used at the navigators position on aircraft such as the Avro Lancaster heavy bomber.
Measures ~3.25 inches diameter and ~3 inches deep. In good condition given its age.