Importance of centering the hand (for when the cane misses poles and corners)
Even when the cane is being moved correctly, it may go around poles and corners without contacting them, giving no warning of approaching them.
However if the pole or corner is close enough to the hand holding the cane, the shaft of the cane will contact it.
This means that the parts of the body that are behind or above the cane hand are protected -- people will be warned if they are about to walk into a pole or corner that will impact their body near the cane hand
(click here for a drawing of the cane and pole).
This page illustrates this with pictures and videos.
The first video below just shows the cane which is used in the demonstration of the second video (it's 50 inches long, moved in an arc 6 inches wider than the body).
The second video shows what happens when approaching a pole with the hand centered, and what happens when approaching it with the hand held off to the side.
In this first example, I am approaching a pole such that if the cane doesn't contact it, I will impact it at my left shoulder, which is not near my cane hand:
Area of coverage, and effect of centering the hand
In the illustration below, the cane goes around pole again, but this time I am walking more directly to the pole (such that if the cane does not detect it, I will bump into the pole with my head, rather than my shoulder).
The tip of the cane still misses the pole but in the last photo, the shaft of the cane contacts the pole and warns me of its presence, illustrating that people are protected from bumping unaware into poles/corners that are approached near the hand.
If the hand is centered, this area of protection includes the face, but if the hand is held at the side, this area of protection includes the hip and shoulder -- the head is unprotected.