My grandparents are diabetic, and I've long imagined an implant that could measure blood sugar levels and report it back when they sit down at the computer or pick up a device. NFC is used in subdermal implants today, it could be done. My grandfather has a pacemaker, perhaps it could be a combined function. The problem would be getting blood samples without actually causing damage to vessels, but I am no medical researcher so I don't know all the hurdles.

I agree with you that measuring is the most intensive task of tracking personal statistics. I can enter how many servings I had of what in any fitness tracker website, but what if I had 1.3 servings? What if I had .2 servings (just a taste)? How do you estimate that without measuring it first? And if you're measuring everything on a scale, where has the fun gone in life? What's the difference between medium intensity running vs high or low? If I biked at 15mph it might be medium, but what if I kept that 15mph steady up steep hills? Or what if I kept 15mph down a hill without pedaling? We're built for rough estimates and are amazingly adept at convincing ourselves we're right.

I have enough difficulty with time tracking at work either breaking my productivity or cutting into my limited "me" time, and that's just a petty little thing. I usually end up estimating at the end of the week then fixing discrepancies that always come up.