I'd like to understand this too!
Like I previously mentioned before math isn't my strong point but my assumptions normally get me a starting point :)
Therefore I'm assuming runtime constants are just "constants" in the mathematical context that there static values, i.e. they don't change?!
Not sure what the collapsing of expressions are maybe there the result values enumerated from the expression?!
In answer you your question tho CakeSpear yes the 64999966*one / 1000000 (one equalling 1) does seem to provide a more accurate result in 64.999966