Sliders

A slider is a device that sets a value.  It consists of a vertical or horizontal bar and a knob that moves on the bar.

The position of the knob in the slider indicates its current value.  Users can move the knob, and thus alter the value, by positioning the cursor anywhere over the bar (even the part of the bar that's covered by the knob) and pressing the left mouse button.  The knob immediately jumps to the location of the cursor.  The user can release the mouse button to fix the knob in its new location, or begin dragging the knob along the bar.

A slider can set values on a continuous scale (between some maximum and minimum) or values at discrete intervals.  If the latter, the knob jumps to the position of the nearest permitted value when the user releases the mouse button.