The hp 40gs is a strikingly beautiful calculator with a charming underlying precept. However, the idea is still a work in progress. I might not even mention it if there weren't a superior alternative available right now at a lower price (the hp 48gii).

I've hardly become an expert in the ten days I've been tooling around with this handsome devil, yet I've already found a few unsettling issues. There may be more.

For example, one nice idea in this OS, as compared to the hp 50g/48gii, is that the user can stay in equation writer almost all the time. In fact you MUST be in the equation writer in order to access most CAS functions. This could actually be a boon for "mathematical doodlers" like myself. After all, a CAS is the main reason to own a calculator like this. Unfortunately, execution is lacking on the concept. Here are some problems with the way the equation writer (EQW) was implemented:

- In EQW -- where you must be for most exact symbolic calculations -- the results appear in throbbing inverted text which is pretty hard to read. You can press VIEWS, to get normal text, but then often it's reduced to a tiny font and you must press yet another button to reach el display sympatico.

- There's no universal Clear key that always works in equation writer. According to the User's Guide, SHIFT CLEAR clears the display -- but not so in EQW. Not always. Closest thing I've found is jumping to HOME, then back again to CAS. Yet the ON/CANCEL key is unused and could easily meet this need.

- PUSH (mentioned in another review) does not round out the system as one would hope. Arbitrary expressions can not be transferred from HOME to EQW. From Mastering the hp 39gs & hp 40gs: "In general the PUSH command is not really very useful." I'm forced to agree.

- Some expressions are not what a trained mathematician would expect. For example, in EQW, enter 4 / 2 right-arrow squared. The result looks all the world like 4 squared over 2. Press the ENTER key and you discover the 4/2 behaves as though it was enclosed in parentheses -- but it wasn't. HP should be really embarrassed by this. (Yes, I know the exponent is past the end of the divide line. That's beside the point.)

- If you exceed the calculating power of the 40gs, and let it run for more than a minute or two, you will get no error message. It will simply lock up and your only recourse is a hard reset erasing the entire history. You may need a straight pin that fits in the reset hole in the back. For example, in EQW, press and hold down SHIFT followed by the square root key four times and then the 1 key. Release the SHIFT key and press ENTER (turn on complex mode, if prompted). If you don't press the ON key within approximately ninety seconds (and you may have to press it twice) you will get the lock up. But this is not an especially tortuous expression, and some expressions actually REQUIRE over two minutes to evaluate.

- Occassionally, the 40gs locks up for no apparant reason. Once again, the history, and all your variables and functions, are toast.

Three of these issues are moot on the 48gii and the remaining three were resolved in various ROM revisions years ago. The 48gii gets its pedigree from the HP's top-of-line 50g. 4/2 right-arrow squared actually encloses 4/2 in parentheses, and even after 10 ... 15 ... 20 minutes on the hour glass, a quick stroke of the ON key revives the 48gii with memory intact. Finally, in nine months of daily use the 48gii hasn't once required a reset.

There are several other reasons to prefer the 50g's paleface cousin, the 48gii. RPN is available just for fun, but it's not forced upon you. You can press the ALPHA key twice for ALPHA lock (on the 40gs you have to hold down the ALPHA key -- which doesn't work for the O key ... issue #322). The ALPHA keys don't conflict with the number keys, as they do on the 40gs, so you can intersperse letters and numbers in ALPHA lock mode. Your entire calculation history is available in one place -- the HOME screen. And even though the processor is only 48 Mhz versus 75 on the 40gs, most symbolic calculations are actually faster on the 48gii. And there's less difference than one would expect for exact numeric calculations (e.g. 40 seconds for 1000 factorial in exact mode on the 48gii versus 30 on the 40gs).

In sum, the 48gii has inherited many generations of ROM revisions from the 48-49-50 line of HP calculators while it seems the 40gs is only two or three steps up from the original 40g. Each new ROM represents thousands of programming man hours, making the 48gii more stable, easier to use, fast, and more elegant compared to the 40gs.

There are a few things that are counter-intuitive on the 48gii which are straightforward on the 40gs. For example, on the 40gs, you can drop an old expression into the middle of a new one by using the up-arrow key followed by ENTER. With the 48gii/50g, you must first press the HIST key, for no apparant reason other than compatibility with EQW mode. (And HIST is mentioned only briefly toward the end of the User's Guide!)

On the other hand, the keystrokes for a function on the 40gs are often entirely different in EQW as opposed to HOME/approximate mode. For example, in EQW you need to press SYMB to get your CAS history, whereas SYMB has nothing to do with history on the HOME screen. This seems arbitrary and adds needless complexity.

Overall, once you get used to it the 48gii is a little easier to crawl around, largely because of the extra key legends resulting from the second shift key -- even though the keyboard seems overly busy compared to the 50g or the 40gs. (Blame goes to the color scheme for that.)

The 48gii has had a USB port since 2006, and as best I can tell this model doesn't suffer from the keyboard issues that plagued early production runs. Even if you do get a bad keyboard however, HP will honor its outstanding warranty policy. I would ignore the irate reviews of yesteryear on Amazon.

If you are intereted in comparing the various models, check out these links:
[...]
However, HP enthusiasts often downplay the depth and power of the TI CAS system for regular algebra and calculus. For some perspective on this, see:
http://b.kutzler.com/downloads/nspire_successor_of_derive.pdf

If money is no object, you will want the hp 50g or one of the TI or Casio CAS calculators topping $100. If you are a student, you should probably get the calculator recommended by your instructor. But in terms of bang for the buck, the 48gii is an especially sweet deal right now, and I recommend it over the 40gs.

The hp 48gii is available through third parties on Amazon for [...] including S&H. And now I see new hp 50g's from a highly rated seller going for [...] with S&H. These amazing deals might portend something new coming round the bend for HP. To be safe, I'd just inquire to be sure you're getting one of the recent USB port models (four AAA batteries in the 48gii instead of three).
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