Samsung has just released an updated version of its health software for the Samsung Galaxy S5 that measures stress levels. Using the heart rate sensor on the back of the phone, the S5 will calculate a measure of stress from low to high. Although this may seem far-fetched to some, the phone is actually using a measure of the heart rate to calculate something called 'heart rate variability' or HRV. HRV has been shown to be related to a range of clinical conditions that include problems with the heart