Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Components (hierarchy name)
4. components (objects parts)
5. [components by specific context]
6. vehicle components
7. [vehicle components by vehicle type]
8. [aircraft and spacecraft components]

Anotations

Scope note:

Flight instruments used for measuring the angle of drift of an aircraft. These have sight wires that rotate until objects on the ground appear to travel parallel with it so that from the position of the wire the drift angle may then be read directly from a calibration chart.