Apple Final Cut Pro 7 - Manual (Page 1117)

When you release both keys, the new relative length and angle of the two handles are
locked.
Hold down the
Command and Shift
keys to change the
length and angle of a
handle independently
of the other handle.
Creating Keyframed Motion Paths in the Canvas
You can create motion for a clip by repositioning it and then setting keyframes to change
the clip’s Center parameter value over time. By setting enough keyframes, you can
eventually create the motion path you want.
There is an easier way, however, which can produce more sophisticated results: you set
up the motion in the Canvas using a motion path (in Image+Wireframe or Wireframe
mode). Once you set the first Center parameter keyframe for a clip in its Motion tab, all
subsequent changes made to that clip at different points in time introduce additional
center keyframes. When you create two or more center keyframes, they appear in the
Canvas along a line called the motion path.
What Are Motion Paths?
The simplest motion path is a straight line defined by two center keyframes. Once the
first keyframe is defined in the Motion tab, any time you move the Canvas or Timeline
playhead to another location and then move that clip’s wireframe somewhere else in the
Canvas, another keyframe is created automatically.
1117 Chapter 67 Adjusting Parameters for Keyframed Effects