Almost everything that you need.
This is a good app that ones hand in hand with learning the music theory required for playing jazz. However, count down timers work better to incentivise users to improve than stop watch functions. Results could also be, at the very least, saved so that progress can be reviewed. Conceptually, graphical representation of results over time would be brilliant. As far as basic functionality, this app does exactly what it sets out to do. Cheers.