Cabin Altitude and Differential Pressure Indicator, F-89B Scorpion

This is a Cabin Altitude and Differential Pressure Indicator as used in USAF's Cold-War-era Fighter/Interceptor F-89 B Scorpion. See photo of the instrument panel from the F-89 B Flight Manual dated 1958, the indicator appears as item 12 on the right side of the panel. The indicator has two pointers one for Cabin pressure/altitude, and the other for Outside pressure/altitude, each which rotate as the pressures change, the differential pressure being indicated by the gap between the two pointers along the index. In the photos the Cabin pointer is behind the Outside pointer and cannot be seen. Measures 2.25in diameter and ~6in deep.