While there are many heart rate apps available, Inner Balance is monitoring heart rate variability (HRV) - a measurement of beat-to-beat changes that occur within heart rhythms and a sophisticated and highly sensitive observation of emotional fluctuations.
They quantify your stress level by calculating your heart rate and the minute variations in the time between each beat, a measurement known as heart rate variability (HRV), which has been used to gauge the likelihood of mortality after a heart attack and to help assess certain psychiatric conditions.