How does this seem to you: Adding Fractions Animation
(Also, I am not sure it is an "animation" or "demo" or what).
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
I would call it an animation. Great teaching aid for fractions. Excellent job!
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.