The current HP-35S is perfectly servicable RPN calculator that you can still get:

https://www.amazon.com/HP-F2215AA-ABA-S ... B000TDRHG8

It works as well as any of the others, with the exception of a pretty awkward hex-decimal conversion scheme. If you do a lot of hex, then, I would highly recommend going out and finding an HP-32S or SII. They have gotten quite expensive (up to $400 for a while before the HP-35S was introduced) but they also work much more easily for base conversions.

I have what amounts to an HP calculator museum in my desk at work, having accumulated various HP calculators over the years, but I end up using the HP-35S or HP-32SII almost all the time, and the HP48G/GX, HP-28, HP-15C, and the like, rarely. At one point, having something you could program was a big deal, but now, I and most anyone else has access to far better computing platforms than a hand-held calculator, no matter how good.

Brett

I was told the C stands for CMOS - the low current drain semiconductor technology, which combined
with the LCD display, means the calculator can run a long long time on a few coin cell batteries.

The C models do use CMOS, but I believe the designation has more to do with the "continuous memory" feature which the CMOS facilitates. The first C models used LED displays (25C, 29C and 19C, 33/34/38C) and rechargeable AA battery packs. In addition, both the 33C and 38C were available with conventional NMOS memory, and those had 'E' designations (the 25C was also available with regular memory, but they didn't give it a suffix, just called it the HP25). All of the LCD models featured continuous memory, and they used the C suffix until the 28C was upgraded to the 28S in 1988.
-Adam

I really like the form factor of the 28, and entering alphanumeric characters is vastly easier than it is on the 48-series, but it can be otherwise pretty difficult to use, with the soft key usage a particular weakness as far as I am concerned. Everything is just a little bit "off" compared to the others - in particular, the soft keys for the 48 series make some sense, and are used for functions that otherwise wouldn't be there. The soft keys on the 28S are used for regular functions, like logarithms and trig functions, which is less than ideal.

BTW, while both of my 28s still work, the ribbon cable going from the alpha to the main halves is somewhat failure-prone, and it's very difficult to repair without destroying the entire thing.

Brett

"The first C models used LED displays (25C, 29C and 19C, 33/34/38C) and rechargeable AA battery packs."

Well that gives rest to that incorrect story!

Thanks for the coments - I do recall that my original TI scientific calculator used LED displays and the
nicad batters pack.

And that thing would run for about three minutes straight before it was 'lights out.'

Typically right in the middle of a chemistry test. This was the first time that seats in the classroom which
were near power outlets were at a premium.

IIRC the battery compartment on the 28 was a real "gem" to close back up again, I don't think mine survived more than a couple of battery changes, before the plastic around the frame cracked and I was reduced to tape to keep the metal bit in contact with the batteries.

https://en.wikipedia.org/wiki/HP-28_ser ... tery_cover

In my case I went to a 48SX, who's keyboard eventually failed. Which I have vague recollections of being a common problem. They're definitely not friendly to disassembly...

It was replaced by a 48G+ (while I still had an actual "need" for a calculator). - Its still sitting in a drawer here, still works. For grins I bought a HP50G a couple of years ago, last of the Saturn line. (and had more or less normal expansion/IO connectivty) Kinda funny as I understand it, its an ARM processor running a Saturn 48/49 rom in emulation mode.

These days, I just use a 48 emulator in the phone. (Also funny for same reason. :-} )

David

I Have a 25, 48G and Had a 41c.
The 48G has a library of useful electronics formula that can solve for unknowns.
PS: it also can be used as an Algebraic Calculator. As I remember!

The last calculator I bought (Nixie Tubes):


The most interesting (Built in DMM):