ODFF: RRI function

1. "Summary: Returns the interest rate resulting from the profit 
(return) of an investment"

That's more or less copied from Calc Help, and doesn't really 
illuminate. How about:
"Returns an equivalent interest rate when an investment increases in 
value."

2. Typo: N and P are both used for number of periods - need one or the 
other.

3. "N is NOT truncated to an integer" - that's OK, but it might be wise 
to note that for fractional N the result is slightly inaccurate, as a 
partial period does not partially compound.

4. I wonder if this function should really be included in ODFF? Calc has 
it, but Excel does not. It's a simple formula calculation, and you need 
to understand the formula to use it anyway.

D

PS I'm almost through looking at functions (as part of another task), so 
this may be the last of these notes. Hope they are useful.