"Adjutant's Call" is a bugle call indicating that the adjutant is about to form the guard, battalion, or regiment.
[1] "Assembly", "Adjutant's Call", and "First Sergeant's Call" are the three bugle calls that make up the "formation" category of bugle call.
[2] The top staff is for the bugler, while the lower staff is for the drums and the cymbals.
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