It limits what on the screen at various speeds so you have no ability to over-read and you can track your speed. I just found out of their existence. I tried this one for a few minutes https://play.google.com/store/apps/deta … &hl=en but I maxed out on the speed that is allowed for the trial and stopped caring because it's in English.
I might be better off without this kind of app but with self control.