Here is another concentration excercise offered by Sri Chinmoy that continues with the theme of using a black dot.

One other exercise that you can practise is this. Make a very small circle on the wall at eye-level, and inside it make a black dot. It should be black; not blue or red or any other colour. Then stand facing the wall, about three and a half feet away, and focus your attention on the circle. Your eyes should be relaxed and half-open. Let the force of your concentration come from the middle of your forehead. After three or four minutes open your eyes fully and try to feel that, from head to foot, you are all eyes. Your whole physical existence has become nothing but vision. Then please concentrate on the dot inside the circle, and start making the object of your concentration smaller. After a few seconds try to feel that your whole body has become as tiny as this dot on the wall. Try to feel that the dot is another part of your own existence. Then enter into the dot, pierce through it and go to the other side. From the other side of the dot, look back and see your own body. Your physical body is on one side, but on the strength of your concentration you have sent your subtle body to the other side of the dot. Through your subtle body you are seeing your physical body and through your physical body you are seeing your subtle body.

When you began to concentrate, your physical body became all vision. At that time the dot was your reality. When you entered into the dot, then vision and reality became one. You were the vision and you yourself were also the reality. When you looked back at yourself from the dot, the process became reversed. At that time, you became the vision there, and the place to which you returned—your body—was the reality. Then, the vision and the reality became one again. When you can see the vision and reality in this way, your concentration is absolutely perfect. When your power of concentration can bring you to the other side of the point which you were calling reality, at that time your whole existence will be far beyond both vision and reality. The moment you can feel that you have transcended your vision and your reality, you will have boundless power.

(Source: Meditation: Man-Perfection In God-Satisfaction — by Sri Chinmoy)

Without concentration and commitment
There can be
No permanent and real victory
In life.
— Sri Chinmoy