What it does
A bansuri is named for its Sa: the note it plays with its top three holes closed and the bottom three open. Hold that note steadily, and the key finder listens: it tells your flute from the room, settles on the note you hold, and names it, C, E, G♯, with how far it sits above or below the tuning most of the world uses (A at 440 Hz). Many hand-made flutes sit a little off it; knowing by how much is how you tune a tanpura, a tabla or another instrument to play with yours.
Keep it as your Sa, and the tanpura, the tabla, the fingering chart and every swara Meend plays are in your flute's key.
In the Meend app
Free on iPhone and Android, with a tanpura and tabla in your Sa, a riyaz page for every raag, and Meend listening as you play.