Pressure Altitude Calculator for Rolls Royce Dart 534-2 Engine (NOS)
This is an interesting little gizmo. It is labeled as an "indicator" for use with the Rolls Royce Dart 534-2 Turboprop engine in 1971, but it is clearly a type of calculator used to determine the pressure altitude. We are assuming it is used by setting the dial at the fuel level on the bottom scale and noting the prevailing air temperature given by the control tower on the upper outer scale, the pressure altitude is read on the upper inner scale.
The Dart engine was primarily used in civilian/commercial transports such as the Vickers Viscount in the 1950-70's.
Knowledgeable visitors are invited to either correct or confirm this information.
Measures ~ 3 in square.