Moving on to a slider. A slider is a horizontal track with a control called the thumb, which you can slide with your finger to move between the minimum and the maximum value. A slider is viewed as an approximate control. For example, a slider is a good control for screen brightness, because users can see the results right away and don't need to be overly precise. Sliding a knob here is a whole lot easier than entering manually some numbers would be. Here's an example of a basic slider with icons added.

And here's an undocumented by Apple example, where the icons change as you start dragging. So a slider consists of a horizontal track and a thump, which is a circle of control that users can slide It can include optional images that convey the meaning of the left and right values. In the case where the user needs to select from less to greater value of something, there is no other hint for that. Use the icons. And of course, the portion between the minimum value and the thumb is filled. If it adds value, create a custom appearance for a slider.

For example, you can define the appearance of the thumb so that users can see at a glance with a slider is active. As already mentioned before, supplied images to appear at both ends of the slider to help users understand what the slider does. Typically, these custom images correspond to the minimum and maximum value of the value range that the slider controls. A slider that controls image size for example, To display a very small image, it the minimum end and the larger image at the maximum and define the different appearance for the track depending on which side of thumb it is on, and which state the control is in. Lastly, a little note for development. Apparently in the code, the volume slider is a different thing.

It's not the regular slider, it behaves and looks almost the same, though.