Calories and the minutes of exercise per day is great to have as a metrics. That basically how much of the world measures their diet intakes and when trying to stay or get into shape. But the third circle, which measures how many times one has stood up each day, while important, does not mean as much to me as something else like how many steps I have taken each day.
What if Apple allows us to customize one or more of those three circles with alternative metrics or add an extra circle just for what?
More at On Apple.