Here is a WWII-era Inclinometer Type B-2, made by Jaeger, as used in the US Army Air Force heavy bomber B-24 Liberator, J-L models. It has a serial prefix of AF43, indicating a manufacturing year 1943.
According to its spec sheet from the Army/Navy Index of Aeronautical Equipment, Vol 6 Instruments dated 1944:
This instrument is used to indicate the angle of the airplane, so bombs may be safely released in bombing operations. This is accomplished by a compound pendulum which is free to oscillate in a plane parallel to the longitudinal fore and aft axis of the airplane. The pendulum is geared to a pointer which revolves in a limited arc on a dial calibrated through the range from zero (level) to 30 degrees nose up or down. When the airplane noses up or down the pendulum remains vertical, thus changing its position with relation to the rest of the instrument. This change is indicated by the pointer on the dial.
There are two small white index markers along the perimeter of the scale (in the photo of the front, one is at the 0 degree position and the other is at Nose Down 5 degree position) that can be set at a target degree range by turning the knob. Pulling and turning adjusts the Nose Down marker, pushing and turning adjusts the Nose Up marker. The knob is missing from its stem but could probably be replaced. On the back is a lock/free screw, that captures the pendulum for safe storage before installation when locked.
It is in terrific condition given its age. The dial markings are clear and the glass and case are intact. The gasket between the frame and glass appears to be missing, so the glass is slightly loose, but secure. Measures ~3.25 inches diameter by ~3 inches deep.