It is rare that users already have BPM data in their iTunes library.
enTrainer’s automatic Beat Detection feature will calculate the tempo of each song in your playlist just as a song starts to play. It may take 5 seconds or so to complete this task, which is why you may notice a change in speed once the calculation completes.
enTrainer strives for accuracy, however some music is challenging. Fortunately, the best music for your activity usually has a steady and pronounced beat anyway, so you should hear excellent results. The song’s tempo will be displayed once the BPM calculation is complete.
The “ratio” shows you how much the music is slowed down or sped up to match your target cadence.