Resizeing stack proportionally

[malte brill]

Hi there,
I wrote the following script to resize my stack in a 4:3 ratio

on resizestack
  set the width of stack "main" to the height of stack "main"/100*133.33
  set the rectangle of image "back" to the rectangle of stack"main"
  set the location of image"back" to the width of stack"main"/2,the height
of stack "main"/2
  pass resizestack
end resizestack

sorrowly the stack starts "jumping around" a bit after being resized.
Is there a more elegant way to scale the stack proportionally?

Regards
Malte