Interval Timer is simple and very easy to use.
If any doubt you can follow in app introducing Tutorials.

Usability -
* Boxing round timer.
* Calisthenics circuit timer.
* Circuit training.
* HIIT training.
* Tabata.
* Yoga.
* Any Exercise.

Pro Features -
* Scientific Calorie counter.
* Daily Statistics.
* Monthly Statistics.
* Statistics Summery.
* Notify by Sound.
* Count by Sound.
* Works great with music and headphones using sound mute mode.
* Motivational Reminder notifications.