The shutter gains speed if the wheel moves up, and the shutter loses speed if the wheel moves down, after selecting the S button on the photographing screen.
You can take a picture without shaking if the shutter speed is fast. However, the picture can be dark, as the amount of light is reduced. On the contrary, if the shutter loses speed, the after image of the subject remains and a unique picture can be taken like a long exposure picture.
Notes