Bugs:
If the block is grabbed to start recording, the cursor from playback doesn’t disappear.

To Do:
Add child/sled.
FBD vectors are often too large for the window.
Make FBD optionally appear in a separate window.

Low Priority:
Move “frictionless” checkbox inside slider area (2nd panel only).
Striped Arrow coordinate view stripes for perp & parallel?
This will be more difficult to implement (and worse performance) for perp & parallel.
Let's evaluate this representation for the Cartesian arrow graphics before pursuing.