Pick:
Pick the particle system that you want to display the velocity for.
Draw Velocity:
Toggles the drawing of the velocity marks. Keep this off as much as possible, otherwise MaxScript will have a tendancy to do Very Bad Things.
See the Known Bugs/Limitations section for more info.
Display Group:
Velocity Flag Limit:
Any particles going faster than this value will be flagged with a red tick mark. The value is in Units Per Second.
Display Scale:
Scales the velocity strokes drawn for each particle. If set to 1.0, the stroke will show the exact velocity of the particles.
Velocity Colors Group:
Simply changes the gradient used to display the velocities. The left color is for particles with 0 velocity, the right color is for the fastest moving particles on a given frame, and the middle color is for the midpoint velocity.
This script is unstable, to say the least, and is stressing Maxscript in ways it shouldn't be stressed.
Because of this, it is recommended that Draw Velocity is kept OFF as much as possible to avoid oddness.
If the velocities suddenly start drawing like this:
Then simply toggle Draw Velocity off and on again.