Metronome
A metronome was a device from Earth sometimes used by musicians to maintain a steady beat they could follow while playing a musical instrument. 

In 2378, Seven of Nine, while in the holodeck, made use of a metronome while playing a piano. ()

In 2380, D'Vana Tendi tried to give a Hiverian metronome to  O'Connor. ()

In 3189, Paul Stamets used a metronome while playing piano to accompany Adira Tal on the cello. ()

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de: Metronom
Music
Tools