HP-65 STD PAC SD-01A Personal Investment weirdness

[John Garza (3665)]

No wonder HP swapped this out for the calendar program.

It seems stuck in a forced progression through time. Meaning it can't be easily used to evaluate your investment options. Try running through once then changing the interest, key in the end date, and see what you get.

There seems to be 2 main issues:

1) Key B requires PV in the y register. And the card doesn't indicate this. And that means if you tinker with y, you're in trouble.
2) At the end of LBL 1, you see the sequence: RCL 2 STO 1 RDN. This makes the new starting date the old end date. So, if you are trying to get numbers on various investments with different returns and maybe different deposits, you would compare in the same time period. This prevents you from doing that. As a quick fix, I deleted those steps and recorded the modified program on side 2 in case I needed it. And note that you will have to manually update the start date for changes along the 'linear investment' mode. For example 12% one year, 16% the next, etc. I just use whichever card side is appropriate.

This is really a simple but useful little program. But it could have been so much easier to use.
Most of the early finance programs are a little weird, until you start getting the generalized TVM programs. HP-67/97 Annuities and Compound Amounts as an example. One of the better ones I've seen for the HP-65 is TVM from PPCJ V2N6P14. It requires 2 cards. One for solving everything but interest, the other for solving interest (as it require a little root finder program)


-J

[Dave Britten]

The HP 80's TVM calculation functions were not at all idempotent either (they operate directly on stack registers as their inputs), so the operation of these 65 programs isn't hugely surprising.

For anybody else that wants to see it, the TVM program you mentioned can be found on Gene Wright's (old?) web site. This is typically the one I reach for if I need to do TVM on my 65.

https://www.rskey.org/gene/calcgene/ann65.htm

https://www.rskey.org/gene/calcgene/ann65i.htm