On Jan 15, 2012, at 4:13 PM, ma...@mohawksoft.com wrote:
> 
> 0.999999999999999 for all intent and purposes is the same a one. And a 0
> with an infinite number of 9s after the decimal point equals one.

This is true for scientific math, but not for financial math.  I find it 
confusing that you make this statement immediately after making the point 
(which I agree with) that financial math is different from scientific math.

Financial math in the US usually is accurate to 3 decimal places, 1/1000th of a 
dollar, because that is the smallest unit of currency defined by the Coinage 
Act.  It's called the mill.  Banks and such don't recognize "a 0 with an 
infinite number of 9s after it" as valid.  This is why 0.9-bar dollars is not 
the same as 1.00 dollars.  There may be a mill missing, depending on how that 
figure was obtained.

A lone mill doesn't seem like much of an error, but remember: every calculation 
based on that figure will be off, and every calculation based on those 
calculations will be off, and so on.

Amortizing an IRA is definitely something that individuals do with personal 
financial software.  We ask "what if?"  What if I add X dollars every year for 
the next five years?  What if I add 3/4 X?  Will that be enough for my 
retirement?  A floating point rounding error will cascade through the 
amortization and throw off the long-term results by noticeable, possibly 
significant, amounts.

I reiterate my statement: wrong is not good enough, not even for personal 
finances.

--Rich P.

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