Assertion: tuba's valve | /r/HasProperty | operated by the thumb
Facets:
value: usually
type: TEMPORAL
Source sentences:
text: It has a fourth valve, usually operated by the thumb, which routes the air to one set of tubing tuned to F or another tuned to B♭.
text: By using a fourth valve (usually operated by the thumb), the horn player can quickly switch from the deep, warm tones of the F horn to the higher, brighter tones of the B♭ horn, or vice versa, as the horn player may choose to have the horn set into B♭ by default by making a simple adjustment to the valves.