I'm a numbers geek. I like tracking and trending things. Crunching data is one of my self-soothing mechanisms. Twice a year, I get the cold hard feedback on how my books are selling. There are indicators I can follow on a more day-to-day basis: review numbers at Amazon and Goodreads, sales numbers at Amazon (though I can only approximate them based on fluctuations in the sales ranking). But in the final analysis, there's data that's only available from the semi-annual royalty statement.