Here's an idea for delta

I noticed that in unity there is a fixed update and a onEnterFrame type update.

Instead of using a set delta, I'm calculating the difference of time between the calls.  Also I made it so you can define fps instead of delta.
Is there anytime that you try to avoid floating point calculations errors while working on game engine parts?  http://stackoverflow.com/questions/588004/is-floating-point-math-broken