Activity tracking is a lot more straightfoward than than measuring learning. The number of clicks on lecture videos or reading activities tells one nothing about what is going on in their heads. On the other hand, regular running is known to improve health, so if my activity tracker says I went for a 5K run each day, then I can be fairly sure I am keeping relatively fit. And if I need further reassurance, I can check my heart rate which is effortlessly measured constantly, and is known to be a good measure of fitness. My resting heart rate is just above 50 and when I was ill recently it shot up to 90 for days, showing just how responsive it is as a measure of stress.. So it is reliable and simple. This just goes to show that although we can be rightly critical of narrow quantitive measures, they can be extremely useful when we know what we are measuring. Of course, I could argue that I did not really need to buy a running watch to know that I run regularly and that this is good for me. The popularity of fitness trackers and the quantification of our lives is, ironically, much harder to understand. In the times before activity trackers or, perhaps, before jogging became a thing, people were much fitter than they are today.