Jerky Animated Graphics

[RM]

I have been messing around with what are, frankly, extremely simplistic, 
experiments in animating
polygon graphics.

However, as I change the vertices of a graphic the thing won't stay 
still but keeps moving its centre,
so I have to keep reseting its left side. As a result while the 
animation is running the whole thing looks
like a horrible, jerky film from about 1880, which, while charming in 
its own way is not what I am
aiming at: a smooth, flowing animation.

I would be most grateful for any ideas on how to achieve that smoothness 
of motion.

Images and stack here: http://forums.livecode.com/viewtopic.php?f=10&t=26858

Richmond.