"thought control" exercise question

[ArtOfHands@...]

I am currently practicing the first thought control exercise of Step
one. 

I need to make certain that I understand the object of the exercise. 
As I understand it, the aim is that during successive days, fewer and
fewer thoughts will appear and the mind will be generally less chaotic.

Have I got it right? I am observing my thoughts as instructed, twice
per day and for a minute longer each day. After each session I am
noting the thoughts that occurred during the session in journal. I
have been meditating for several years, so I am not deluged by
thoughts as I might have been if I had never meditated.

I certainly know that I have not mastered this exercise yet, because
little has changed from day to day. However, how DO I know when I
have mastered it? I'm not in a hurry, I just want to know.