When light ผ่านสลิ pair will see a dark bar and bar light switch. When the distance of one pair of channel change. The size of the bar, dark and bright bars would change. A pair of ถ้าสลิ distance between channels is small. To see the dark bar bar light with wide range very wide. But ถ้าสลิ a pair distance between channel endorsements. To see เถบ dark bright bars smaller and closer.