I'm using the Microsoft Health app on my Lumia 950 to count steps taken. Even though I do not have a Band, the app also shows me calories burned, but I'm having a hard time figuring out how it's coming up with those numbers. Initially I thought it was using some average value per step taken, but I've also seen the app claim I've burned hundreds or even several thousand calories on days when I've barely taken any steps. Observe the following two screenshots, taken on separate days:
As you can see, steps taken vary by an order of magnitude, whereas calories burned are in the same ballpark.
So how does the app calculate calories when I do not have a Band to directly measure that?