A:Answer The optical HR sensor uses light to penetrate the skin and estimate the heart rate. There are tips to achieve the best available accuracy, you can find those tips here: http://support.garmin.com/support/searchSupport/simpleCase.htm?caseId={1ae59670-f437-11e4-dfa6-000000000000}&kbName=garmin
The steps have a feature called Custom Step Length, this enables personalized step count. In order to use this feature, the user will need to walk or run a known distance, counting the steps it took to complete that distance. This option is recommended to achieve the most accurate information.
Lastly, calories on the vívosmart HR are based on Heart Rate, Activity Class, Gender and Weight. Thank you! ~QKO