Why might I want to alter the shape of the curve between two key
frames?
The shape of the curve dictates how the motor will move between adjacent
key frames. A straight line between two key frames causes the motor to
move at a constant speed. If we desire to have a motor slowly accelerate
out from one key frame and into another, we may dictate the nature of
this movement by shaping the curve with the key frame handles. For
example, say you want to have the slider come to a stop, and then move
the opposite direction. By shaping the curve with key frame handles, you
control the rate by which the slider slows down, stops, and moves back
the other way. The curve shaping tools provide you the ability to create
organic motor movements.

The shape of the curve between adjacent key
frames may be modified by activating options via the Graph Options menu.

The Locking options allow one to move key frames around the graph. The
Handle Style options facilitate shaping curves between key frames.

To modify the shape of a curve, uncheck the Lock All option. Now double
click on any key frame and the curve shaping handles appear. Dragging
the handles around adjusts the shape of the curve. Notice though that
each handle moves independently, and only in a horizontal direction.
This is because the handles are neither linked nor cusped.

If we click on Graph Options again and check the Link Handles option,
the handle positions will now be linked together. For example, moving
the left handle will cause the right handle to move an equal distance on
the other side of the key frame. Notice though that the handle movements
are still confined to horizontal movements.

To allow the handles to move vertically, click on Graph Options again
and select the Cusp Handles option. Now key frame handles are free to
move in either horizontal or vertical directions.

By adjusting key frame positions and curve shapes, it's possible to
create a variety of motor move behaviors. As more motors are added to
the system, they appear as buttons in the axis button region. By adding
key frame positions to multiple axes, it's possible to create complex,
coordinated moves involving slider, pan, tilt, focus, and zoom motors.