Logically, if you're not using some kind of "smart" controller, then you either water manually, or you water according to a schedule with a regular controller. Those are both reasonable baselines, but they would require to user to input those parameters during setup to give a basis of comparison.
But even absent that, the "evapotranspiration" calculations don't appear to be all that mystical. My Rachio, on a flex schedule, really doesn't do anything more than delay the next scheduled watering if there's been rain or there's rain forecast for that day. My schedules run at the same time when they do run, which suggests to me that it's barely more intelligent than that. A "smart" system to me would be running at different times of the day as needed to keep the plants in a good range of hydration. If it's especially hot, it might throw in a late afternoon watering, maybe. But that's never the way it works. I also never notice it doing multiple short soaks in a zone like I remember reading it was supposed to do to help prevent runoff before water could soak into the soil. I'll admit maybe because most of my yard is pretty flat.
Don't get me wrong, I like Rachio, it's a great controller and having the app to control and monitor my system, I just don't know if I believe many of the claims of how "smart" it is. I always have faith that they can provide more and better features and intelligence through updates. That's the great thing about having connected devices.