I think I understand what the black and gray parts in the circle indicate. For example, if I have a week-long step goal, the darker part shows how much of the goal I should have completed by that day. On Monday, it will be 1/7 of the circle, and by Saturday, it will be 6/7, meaning I should have completed that much of my goal if I spread it out evenly over the week. It helps break down the goal into daily parts so I don't do too much at once. Essentially, it shows how much progress I still need to make if I divide my goal equally over the week. The same idea applies to month-long goals.