Total calories burned consist of two components: your Basal Metabolic Rate (BMR), calculated from your inputted basic information, and Active calories, calculated from your daily activity.
BMR indicates calories burned for body life-sustaining functions. Active calories refer to the calories burned during physical activities, separate from the BMR.
If the device is not worn, calories measurement is performed for the basal metabolic rate component only. BMR is determined using the basic information you've provided.