Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Furnishings and Equipment (hierarchy name)
4. Sound Devices (hierarchy name)
5. sound devices (equipment)
6. [sound devices by function]
7. tuning devices

Anotations

Scope note:

Tempered steel instruments consisting of a stem with two prongs, producing a musical tone of definite constant pitch when struck and serving as a standard as when tuning musical instruments and performing acoustical experiments.