my box keeps wiggling between:
This shows up visually on some browsers, not always on others.
It was wiggling on safari when my contents were a gravity form.
It even started wiggling on chrome when I used an image with width=100%.
Perhaps you could make it only recalculate upon opening and upon window-resize as opposed to recalculating all the time?
Let me know if you need help with this, or want some code / patch. I'll likely start working on this now to see if I can get it fixed.