The key is to develop a few solid criteria that you are going to isolate and track from student to student and day to day. These are a little like when a doctor asks “how does it hurt on a scale of 1 to 10.” It’s not that 8 has some unchanging in-the-eyes-of-God meaning. The point is that you can begin to get some quantifiable grasp of your changing perceptions by gathering multiple entries over time.