In a case of a sudden cardiac arrest one should know what to do and how to do it. Numerous studies have shown that the correct CPR increases the likelihood of survival and recovery.
This app is giving you a rate at which CPR should be done in order to maximise a positive outcome, which of course cannot be guaranteed, since you are dealing with a stopped heart. But doing the right thing at the right time is better than nothing.
The rate is based on studies of theCenter of Resuscitation Science - University of Pennsylvania - and numerous studies all over the world.