Download it for use on both Iphones and Android phones at this website:
You simply download the app, select your voice/instrument, set it on your stand or binder while you sit and practice. Every so often, refer back to it and watch to be sure the notes you're producing MATCH The notes on your music, and that the tiny arrow is as close to the center line as you can make it.
See below for all the instrumental & vocal options available so far!
[Baritone is the instrument, not the voice. Vocal baritones should choose Voice (Bass Clef).]