I figured it was more like a dial on a radio. You can't instantly go from 91.9FM to 107.3FM. You have to hit all the ones in between.
The action can be thought as though you are spending time actually listening in to the broadcast (which is how you can gain information about what is coming) so you can turn the dial to any frequency.
The instructions say scratch “a” box below. Compare this to the instructions about taking exposure which talks about scratch the next box.