Looks like an HP calculator forum got to the bottom of this around a month ago. The company HP licensed their calculator production to accidentally shipped a run of units with buggy firmware. Most have been captured and flashed with corrected firmware. Some distributors were unwilling to return their calculators for rework, which is how these ended up in the hands of customers. Anyone with a buggy calculator should contact HP calculator support for a replacement. https://www.hpmuseum.org/forum/thread-21965-post-190853.html...

I wish more was spent on trying to verify the authenticity of the hardware, or contacting HP for comment. The simplest explanation is that a distributor in Brazil sourced counterfeit hardware. Authenticatic hardware shipping with some bespoke and defective firmware seems even less likely than simple counterfeiting.

Unfortunately no trig functions, or this would've been useful: https://www.rskey.org/~mwsebastian/miscprj/models.htm

But running this may be possible: https://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.c...

Wikipedia says there are several clones of the HP 12c in Brasil. They look not 100% the same but cost much less. So maybe someone make HP look-like models and sell they with for a much better price.

HP did license out the manufacture of 12cs at some point so if it's not a counterfeit it is almost certainly a manufacturing error by some licensee. Note that the 12-c is one of a legendary "voyager" series of HP calculators which have that landscape form factor and are highly prized by collectors. There is an HP15-C scientific calculator equivalent and a 16-C which is supposed to be for programmers so does the sorts of things we programmers do all the time like converting things from hex to octal etc. It has built-in support for bit twiddling and shifting operations too. If you ever see a landscape-style "voyager" HP calculator in a junk shop or whatever and it's not a 12-C (because they are quite common) it's quite rare and may be worth buying and reselling if it's in usable condition.

I have 2 HP-12c calculators which I bought while I worked at Goldman. One was always on my desk at work and I had another at home. I can certainly confirm they were common in finance back in 2000-2009ish. That said even back then they were being replaced by non-RPN calculators for a lot of people and only people with nostalgia and the hardcore had a 12c.

They're incredibly robust - famously a zookeeper once used an HP12-c to calculate proportions for animal feed, dropped it into the mix and it passed through the digestive tract of a hippo. It was still able to calculate the yield to maturity of a bond after cleaning.

In addition their batteries last forever. Even though the versions I have use the "weak" newer battery tech[1] they are both still on their original batteries and as I say mine are about 20 years old and at one point I used one of them every day. Having a slow cpu means they just run forever.

I now additionally own two other RPN calculators which I bought because I needed a scientific calculator and have a nostalgia for HP calculators because I used to write little programs for my dad on his. The 12c and the like don't have trig functions in particular so I own an HP35s and a swissmicros DM42[2], which is essentially an HP42S emulator with a faster processor and some enhanced capabilities based on Thomas Okken's "Free42"[3]. I would strongly recommend the DM42 for anyone who likes HP-style RPN calculators and wants a more powerful version. It's a fabulous calculator. Pretty much the only way the HPs are better is the feel of the keys which is too stiff on the DM42.

The HP35s is a great calculator also. Not as powerful as the DM42 but with that lovely classic HP key feel and a bit more usability for some things at the expense of being much worse to program, much slower and only having a 2-line screen. It does have a nice built-in set of physical constants though (which I never use).

[1] The original battery tech uses some sort of legendary toxic battery that is no longer permitted due to hazardous chemical regulations.

[2] https://www.swissmicros.com/product/dm42

[3] https://thomasokken.com/free42/

I wonder how the NPV algo is done.

Prima facia, the way Id tackle it if I have a few extra registers is

1. Id write the exponent as n = R*m, where R is an integer. R = 2 is probably best.

2. Then Id do pascal's triangle (every element is a simple combination comb[x,y]) for the expansion of the exponent (if R = 2 binomial expansion) and add in ascending order.

3. Then raise the answer to the power of m.

Of course, I can iteratively do steps 1-2 if the interest rate is very small.

Was it not known since the 70s that you should never ever use floats for currency? Why would any sane person build a financial calculator using floats?

This aroused my interest:

> describing some difficulty changing the decimal point to a decimal comma on a new Brazilian-bought HP-12c

Perhaps some wrong constant has been put in the firmware as a result of mixing up the command and period.