TVM accuracy revisited Message #1 Posted by Tommi on 3 Sept 2003, 3:13 a.m.
Heylo!
Was looking for a good TVM program for my HP41CX and found the improved FI (FIN) program in PPC Journal 1983 Jan/Feb, p.22f. Great program btw :)
In another thread, the first accuracy problem presented in the PPC article was discussed. What is really the most "correct" answer here???
According to the PPC article, the HP12C in those days returned FV=1,244,458.491 (in the previous thread, the incorrect FV=1,237,786.903 is mentioned for 12C/P, but the payment period is BEGIN, not END).
The PPC article goes on to calculate the troublesome interest rate using the super accurate function
(((1+i)^n)1)/i, where n can be fractional (available on e.g. HP37E in those days, but not 12C or HP41). This will give FV=1,244,458.519.
(The above function do exist in 12C, but only works with INT(n). What about 12CP?)
The improved FI (FIN) program for HP41 presented in the article, will give FV=1,244,458.520, using the accurate E^X1 and LN1+X functions available on the HP41.
Interestingly, my HP49G emulator (ROM version 1.18) returns FV=1,244,458.523.
Do we have 10 significant digits here somewhere for FV?
 HP12C : 1,244,458.491
 HP41C : 1,244,458.520
 HP37E : 1,244,458.519 (returns same as 12C in normal use)
 HP49G : 1,244,458.523
