I've got myself confused with TVM results when using my HP19bii+ v my HP12CP and non-interger "n" (my wife just says, "why have two calculators" - which is a reasonable point however my secret is that I have three (also a HP10b - which gives the same results as the HP17bii+).

For instance if I run a scenario of:

P/YR = 1

n = 2.5

iP/YR = 10% (those were the days!)

PV = 100

PMT = 10

END MODE

HP17 bii+ FV = -153.81

This seems quite reasonable as it is approximately the same as replicating the inputs for 30 months (slight compounding difference I can cope with that).

If I run the same inputs for my HP12CP I get FV = -148.05

Now, reading the manual, I thought this was because the 12CP would take the "0.5" of "n" and consider it as half a month, ie 15 days. But if I try to model a 15 day period (ie P/YR = 24 and PMT = 10/24) followed by a two year period I get FV = -142.99 (which feels about right, but is a country mile away from the 12CP).

Can anyone shed a little light on this for me.

Thanks in anticipation.