HP 12C & HP 12C Platinum - Differences
As the HP 12C Platinum was built upon different mathematical models to the original 12C there are some differences in behavior between the 2 products.
IRR Roots finding:
The HP12C & HP12C Platinum utilize different algorithms to find the answer to IRR. Occasionally, the 12C Platinum will return a different answer to the 12C. This may be the case where there are multiple answers to an IRR calculation.
There is nothing wrong with the answer given (if they differ) it is just a consequence of different implementations of the algorithm.
-100 or 100 as a result of IRRs:
A user may call support saying that the calculator is defective because it always returns 100, or -100, for IRR calculations. This would occur if the user is conditioned to enter cash flows on the 12C in a particular manner; one that is against the entry method advised in the manual.
The 12C Platinum utilizes the value stored in CF0 (the first cash flow) when it performs the IRR algorithm ALL THE TIME. The impact of this is that when CF0 = 0, the 12C Platinum finds a spurious root (an incorrect answer), either of 100 or -100. This is different behavior than the 12C.
12C users may be accustomed to entering all their cash flow by pressing: g cfj and never entering the first cash flow into CF0. It is not normal behavior and against the information outlined in the manual, but it might be possible that the user is conditioned to enter values in this manner. When these users mimic this behavior on the 12C Platinum they are likely to come across different answers!
It is of utmost IMPORTANCE that the cash flow 0 be stored in CF0.
When guiding users through be sure that you use explicit terminology. Do not say: Enter The First Cash Flow, say Enter Cash Flow 0 by pressing g CF0. Ensure that they put cash flow 0 into the calculator by pressing g CF0, confirm that they did not put it into CFJ. This is extremely important. Here is an example:
-200,000 g cf0
-600,000 g cfj
3,000,000 g cfj
4,000,000 g cfj
20,000,000 g cfj