Yet another pocket RPL idea...


So, I'm thinking about how a pocket RPL calculator could be done. (While I don't really do programming on my 50g, I do like using an RPL calculator. And not just because of the infinite stack. I just wish the thing were smaller.)

The basic idea would be a hybrid between the 28C/S capabilties, the 48S/SX/G/G+/GX keyboard, and something like a 42S or even smaller form factor.

(This thing, I know HP wouldn't ever produce it. However, who says someone else can't? There's enough public documentation out there that it's likely possible to make something that's compatible with user and potentially even system RPL, without infringing on HP's intellectual property.)

So, the first thing is... make keys smaller, and go back to a 4-line display. With modern technology, this'll make a nice small handheld. I actually like the keys on my BB Curve 9300 a lot, for tactility, so something like that (but bigger, preferably) would work nicely.

As for keyboard layout, a few changes that could be made:

  1. Menu disable button. On a 4 line display, this is EXTREMELY useful for viewing more stack.
  2. Move the arrow keys up into the softkeys, and they're functional whenever the menus are disabled. This is how the 28C/S do it.
  3. If possible, remove a row of keys, merging all of their functions with the remaining keys, and moving keys into a logical layout. This'll allow keys to be a little larger, or reduce the form factor further. It'll also be only one row more than the 42S and other calculators that are known to do it.
  4. If you do 3, then you might have to move Alpha keys around. Potentially a 42S-like solution as an OPTION (not necessarily a default, or maybe a mode that uses both - when hitting Alpha, you get the alpha menu and the alpha keys work as well, and hitting an alpha key gives you 48/49/50-like behavior and the alpha menu goes away, whereas using the alpha menu gives you 42S-like behavior) would work, too.

Hardware... use an ARM7 microcontroller that has a built-in LCD controller, and you're good to go, CPU-wise. LiIon battery would be nice, with USB charging and data, but a couple button cells would probably work, too. (And, you could underclock it significantly to save power - if you're doing a re-implementation of RPL, rather than using HP's actual firmware, you don't have the emulation overhead that the HP calculators have.)

Theoretically, I'd think this thing could be in the 35s pricing ballpark, maybe a little more, if you didn't have to worry about cannibalizing 48gII and 50g sales.

So, anyone interested in making this happen? (For that matter, that includes HP.) Unfortunately, I don't have the skills to make it happen, just some ideas for something I'd like to see.


For me, the [iPod Touch + Free42] combination provides a current, supported, pocketable (and eventually replaceable) RPN calculator that I use everyday without carrying and risking my physical HP42S. There are many emulators for different calculators on the Apple iOS platform, including at least two for the HP48; some of them are free or have a more than acceptable price tag. There are some for Android OS too. BTW, I also run Free42 in my cellphone, but it doesn't look or feels as good as on the iPod Touch 4G. I know Blackberry has an application development environment, perhaps you may find a suitable emulator for your BB.


The BB is actually my work phone, my personal phone is (currently) a WinMo 6.5 phone, and I have Emu48 on that.

I prefer real calculator buttons when I'm calculating, though.


I prefer physical keys too, but I'm getting used to the iPod (4 Gen) touchscreen and display resolution.


Hi Andres. I agree with you that iPod Touch + Free42 is a good solution. I also enjoy using GO-21 which emulates an HP 21 on the iPod Touch, iPhone and iPad. GO-21




Hi John!,

Well, I have some 10+ emulators on the iPod, but Free42 (or 42S) is the one I use the most. Of course, I would like to have physical keys or, at least, some kind of vibration as feedback (as my Android-based cellphone has); but it's rather useable. Best regards.


Your "hybrid between 28 and 48" is exactly what ND1 is, so your post certainly stroke a chord with me.
Check out the link in my other "RPL kid" post, and see what keypad decisions were made.

The project you're proposing would be very sweet. I don't think HP would go for it, though, because, if they went through the trouble of starting a new generation, they'd want it to scale. At the top of the line needed to be something that's more powerful than a 50g, and creating that (from scratch; required to make true progress) is, I think, a big challenge.

I wouldn't be surprised if someone discovered that the market for such an RPL thing is not worth it. RPL is aging, and not many users seem to be interested in programming these days.

Plus, like it not, it's really an app-world now.


Huh. I see advantages and disadvantages to ND1's approach, but it looks quite impressive. (And, an Android version coming up? Sounds like, when I replace the WinMo pile of garbage with something Android-based, I'll have this up front and center on my home screen.) And, I don't even care about the CAS, so this is perfect. (Honestly, I use my 50g like a 4-banger with an infinite stack, and seamless unit conversion, most of the time.)

I still like real buttons, though... but, the fact that you've reimplemented RPL from scratch means that it's definitely within the realm of possibility, given enough time and resources.


I like real buttons, too. Especially for number keys and basic operators.

But for writing code (RPL or JavaScript), I tell you that I quickly (within a day) much preferred a QWERTY soft-keyboard over small/crammed physical keys. It works even better than on the Kindle, for example, which has a pretty generous keyboard.

Being able to scroll through code and position the cursor at a touch of the finger, is so much better than fiddling with cursor keys.

As for unit conversions. Unit support is about the last thing that's still on HP-28S level. There'll soon be a Units object that will permit you to enter "5cm" and then simply touch the unit badge next to the object (looking like the Color, BigNum, or Chem objects in the doc) and choose from a list of applicable unit conversions.


> but, the fact that you've reimplemented RPL from scratch means that it's definitely within the realm of possibility, given enough time and resources.

Yes. Using the JavaScript approach. I'm a C++ guy, but I swear this would not have been pretty using another approach.

If I were in the hardware business, I'd put my software on a minimal 4 inch EInk minimal Webkit-browser-machine (running some kind of embedded Linux), with a ~15c form factor (maybe just a little larger). Touch-screen would be very nice, but wouldn't be a must (depending on cost).
A color display is pretty useless in a calculator. (Even though ND1 has a Color type...) A screen that can be used outside and sips battery would be so much nicer. A device like this could go a month on a charge.

Edited: 21 Mar 2011, 8:13 a.m.


Oh. And it has to have Wi-Fi.

I think what has largely obsoleted the high-end calculator (outside the education niche market), is that it's been, so far, an island.

Have a powerful code-compatible desktop system and let the calculator be the faithful, mobile companion (with one-button, one-second data exchange between the two; like in ND1 today), and you have, in my mind, a new reason for a high-end calculator.

Sell it for $79 (w/ EInk display and physical keys), and everyone will want one.

Make incremental money with selling specialized code libraries, and create a little app-store for 3rd parties to participate. A platform cannot be successful in isolation. (Even if it's from HP.)

There's nothing wrong with keeping RPL, btw. It's lovely to script JavaScript...

Edited: 21 Mar 2011, 9:01 a.m.


Hmm, maybe the best option would be something that combines the modern slider smartphone form factor with some 28 ideas, then, and doing things a bit in reverse.

Have a portrait form factor calculator with the most commonly used functions on the keypad, and a 320x240 display or so. Except it's not really 320x240... slide the keypad off to the side, and it becomes 320x640, with the 320x400 area that's been exposed as a secondary keypad that customizes itself for whatever operation is currently being performed.

Another way I've thought of is to just rip the 28 off, with a slider to hide the alpha keys when in normal operation.

And, there's also going for a ClassPad/Xpander-like approach, where there's a decent-sized touchscreen and a very simple dedicated keypad for number/primary operation entry.


Your slider ideas sound lovely. Though purists (and many HP followers are; and we're talking RPL (an HP thing), here) may not go for it, on account of the potential flimsiness aspect.

But I think you cannot ignore the reality of price.

If it's a dedicated calculator it will sell in much lower quantities than a generic slider-phone. What you're describing sounds more like a mini-tablet, actually. If you need the calculator to be at most half the price of a fully-fleshed small tablet (which may come down to $250 sometime this year; already there's a glut of Android <2.2 devices with capacitive touchscreens (which suck), that you can pick up for $130-160), I fear you cannot afford that kind of hardware.

If I were HP, I'd try to build this with as little HW mods as possible to the existing range. Just a different screen and different keys. Optionally, a low-res touch layer could provide support for soft-menus and soft-keys. (And serve to bring the key count down and give space to the larger screen.)

All just idle dreams, of course. I see no-one but HP actually pulling off building such a new high-end calc.

(Regardless of RPL being a subject here or not, I'm not counting in TI, because they've already chosen their approach: a clunky brick for education, that will probably not be treasured 20 years from now...)


I was going more for something like the HP Xpander, the Casio ClassPad, or the TI PLT, although a smaller form factor.

Being a dedicated calculator, it could get away with a lower-cost (or, more calculator-suited - e-ink would be AWESOME on a calculator) display, with resistive touch instead of capacitive.

Still, soft-keys like the 28/48/49/50 line and the 42S can work well, too, to help reduce cost.


Thanks for those links, bhtooefr.

I had heard of the first two, but never seen them.

Boy, they're ugly. (The new nspire cx, in contrast, looks like 300% overkill to me (though I get the point about its use in education), but very spiffy/good-looking.)

I hadn't thought about this too much, but I come to realize that my personal preference (and I realize it may be way off from what other people want), is pocketability. That is, not much larger than an iPod touch. And about that thick! (That is, very thin.)

Anything larger, you lose pocketability and may just as well make the jump to a tablet.

Continuing to dream, that leaves two options:

- No keys, but a big touchscreen. Something like an iPod touch, with color display swapped for an EInk display. (And 1 GB flash shall be ok...)

- Half and half: 320x240 touch display with equally-sized bottom area for basic physical keys. Soft-menus, on-screen soft-keys.

I bet this sounds very unattractive for any company to build.

An iPod touch with a slow EInk display?! What the!

The "only" advantages over a smart device (iOS, Android, whatever) would be a lasting battery and a display that displays while it's off (I absolutely love that part on the Kindle...).

Back to reality, I did a search for the smallest e-reader. 5" is actually the smallest (Pearl) display that EInk currently produces (though they'd manufacture anything if you're buying enough units, I'm sure). They're ugly as hell. One is nice and has a touchscreen: The Sony Reader Pocket Edition.

An RPL calculator on that would be nice, IMHO. (Though I'd still prefer smaller.)

Edited: 23 Mar 2011, 10:17 a.m.


Yeah, I'd want pocketability, too - but that basic idea, just smaller, would be interesting to see, I think.

And, let's face it, a 50g is ugly with its array of buttons, if you're using that definition of ugly.

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