Silhouette Handbook of US Army Air Forces Airplanes TO 00-40-1 1942 Luftwaffe the horizontal pointer is exactly

the horizontal pointer is exactly on the middle luminous point

VBC (Vertical)

The small protrusion right of the digit display counter was likely used to reset the counter to zero once pressed

The Air Position Indicator System was an advanced navigational system introduced during WWII in later versions of the Boeing B-29 Superfortress Bomber by the US Army Air Force

The D-1 Pitot Tube had two designs

Silhouette Handbook of US Army Air Forces Airplanes TO 00-40-1 1942 Luftwaffe the horizontal pointer is exactlyHere is an original WWII era recognition manual, the Silhouette Handbook of US Army Air Forces Airplanes, dated September 1942, Technical Order No 00 40 1. The manual illustrates 48 aircraft of the USAAF in service or experimental as of Sept 1942, including combat aircraft B 17E, XB 19, B 25, A 20, P 35, P 51, cargo and liaison aircraft, and training aircraft. Each aircraft is illustrated on a dedicated page. The 8. 5 x 11 inch manual is in good