The most useful thing by far that I have is a good email archive, going back 30 years, and well searchable. Also an OCR’ed archive of pretty much every piece of paper in my life. As far as data goes, I find my real-time dashboard of email backlog as a function of time pretty helpful. Oh, and I also find my count-up timer of how long I’ve been asleep useful. Other personal analytics I end up accumulating, and then look at if I have a specific question.

Actually, there’s another thing: I’ve noticed that a day or two before I get sick with a fever, my heart rate seems to go up. However, in an example of how difficult medical science can be, I’ve (happily) only gotten sick 3 times in the last 3 years or so since I’ve been continuously measuring my heart rate. The first two times I saw this effect. But the most recent time I don’t think I did, though it was hard to tell because other things were affecting my heart rate…