|Re: TVM bug in HP 20b?|
Message #5 Posted by Daniel Castro on 11 Dec 2009, 4:05 p.m.,
in response to message #4 by Gene Wright
Solving for N when the interest rate is zero is a division problem: PV divided by PMT = N.
Yes, maths are amazing :D
Obviously I donít think many people ever use the financial functions for such calculation on real life (I myself found it while playing with the calculator). That might also be a reason about why nobody has informed about the error before (or at least I couldn't find anything on Google before posting here).
All in all, this is not a problem that will cause a probe to crash on Mars surface, but a bug is a bug ;).
2) The NPV function itself works FINE with a 0% interest rate.
Yes, NPV calculation in cash flow analysis works fine, as it does any other TVM analysis with I%=0. As a matter of fact the buggy scenario is a particularization of a payback analysis on a cash flow with an initial investment, constant inflows and no interests (or flows increasing evenly at I% rate). Luckily the payback function on the Cash Flow works fine AFAIK.
My intention was to check with others if this bug was still present on the new firmware version, as I have the old one (including the logarithm bug) and wanted to know if it worth the time to build a serial cable to upgrade it... now I see I can live without the cable unless HP decides to correct this and release the new firmware on their SDK.
Anyway, thank you to you all for taking the time to check this. I will contact HP's customer support to let them know about the bug.