Very simple:
Know what shruti you are checking your voice or instrument for
Select that shruti on the screen.
Sing a swara in that shruti or play a note on an instrument.
Detected swara name is shown on the screen as S, R1, R2, G2, G3, M1, M2, P, D1, D2, N2, N3
The guage shows how accurate you are. If app indicates you are in green zone on the moving needle or strobe bar, then note is accurate.Â
Happy Tuning!