One of Apple's iPod control systems. the Click Wheel is present on the 4th Generation iPod, iPod Mini, iPod photo, iPod U2 Special Edition, some iPod nano generations and (to a certain extent) the iPod shuffle.
3g nano clickwheel

Click wheel on an iPod Touch nano 3rd generation

This is where the select button is in the middle, the next song is the button on the right of the circular control system, the previous song button is on the opposite side, the menu (or back) button at the top, and play-pause at the bottom. To scroll down, move your fingers in the clockwise rotating way around the select button, and anticlockwise for the scroll up ability.

Sources and References

Wikipod: Click Wheel

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