Abstract: An aircraft altimeter-encoder is provided with an altitude sensitive barometric or aneroid bellows which simultaneously drives a visual altitude indicator and an altitude digital encoder. The indicator includes one or more pointers that register with a dial. The encoder includes a wheel or disc having a series of transparent and opaque regions scanned by photo-optical means. This generates digital signals corresponding to the altitude indicated on the face of the altimeter. The digital signals are adapted to be fed to a transponder for telemetering to a ground station. The altimeter-encoder includes means for simultaneously adjusting both the indicator and the encoder disc to compensate for variations in the local or ambient barometric pressure. Means are also provided for adjusting the relationship between the indicator and the encoder disc whereby the digital altitude signals coupled to the transponder correspond exactly to the altitude indicated on the face of the altimeter, referenced to 29.