I have to read into this answer a lot. Would it be accurate to say that the app calculates a "target" respiration rate, then provides visible or audible cues (e.g. a metronome) to tell the user exactly when to inhale/exhale? So the "actual" respiration isn't measured, but that isn't very important as it's quite trivial for a user to follow "inhale now", "exhale now" cues to the necessary degree of precision.
Did I understand that correctly?