Hello,

Quote:

1000 invested at 8% compounded annually to reach 3670 should

equal 16.89 periods, my 12c says 17 periods

You'll get the 16.89 on the HP-38C, which was the HP Financial

Calculator(HPFC) just prior to the 12C, and also on the

HP-18C, which was the HPFC that followed the 12C.

I just found my old program for the 12C which makes it also

give the 16.89. I call it the "pulveriser" as it takes i and

PMT and creates tiny but equivalent replicas of them :-).

Here is the pulveriser, in 15 lines:

1 [n] [STO][PV] [FV] [X<>Y] 0 [PMT] [FV] [RDN] [n] [i]

[RDN] [FV] [PMT] [g][GTO]00

For your case where PMT=0 the above could be simplified of

course, or you could just calculate n as LN(3.67)/LN(1.08).

Or, try this, where [R/S] runs the pulveriser:

8 [i] 0 [PMT]

[EEX] 9 [R/S]

1000 [CHS] [PV] 3670 [FV] [n]

[EEX] 9 [/] ->16.89215375

This method also works for calculating n for non-zero PMT.

Ironically the method used in the pulveriser above does *not*

work at all well on the HP-38C or the HP-18C (or in fact any

other HP TVM implementation). One could argue that it

is not of course needed on those machines, but it is also

useful for finding equivalent effective rates of interest and

PMT in real life - with a factor if 12 or 52 for example.

Anyway, while I too found the n-solving on the 12C unexpected,

I am at least pleased to report that the 12C represented a

peak in HP financial mathematics knowledge/implementation. For

example, look at what you get for i when trying this on HP TVM

programs:

[EEX] 9 [n] 1 [PV] 0 [PMT] 1.05 [CHS] [FV] [i] [RCL][n] [*]

On the 12C we get:4.879016417 (exactly 100*LN(1.05))

On the 38C we get:4.800000000

On the 18C we get:4.87900000000

On the 49G we get: the same as the 18C

On the 200LX :4.8790164000000

It appears that when HP re-did their TVM application for the

18C, they went back to the 38C microcode. Our 12C stands

alone! It has an aura of reliability, not without reason, and it shows in delightfully unexpected ways.

Cheers,

Tony