unmeasured tremolo slashes: how many?
Although some contemporary composers insist on 3 (or more!) slashes for unmeasured tremolos regardless of the note value, best practice dictates that the 3-2-1 rule be applied:
In situations where reduced slash usage may be ambiguous—such as works that also contain measured tremolos or passages involving short note values—consider adding the indication trem. above the staff for maximum clarity.