Welcome to a revolution that never happened.

The HP Xpander was touted as a revolutionary new learning device back in the year 2000 when its name was first mentioned in HP educational catalogs and brochures. What the brochures didn't predict was that within a few months, the project will get cancelled and beyond a small preproduction run, no additional devices will ever be produced.

If the Xpander reminds you of a PDA, the similarity is not superficial. The Xpander is, as a matter of fact, a Windows CE device, complete with touchscreen and stylus. A Windows CE device equipped with a graphical application suite that can help you perform scientific calculations, graph functions, explore geometry concepts, or do statistical computations.

The concept: a minimalist four-function keyboard, a standard 240×320 monochrome LCD display, and a multifunction softkey applet that lets you invoke mathematical functions and operators or enter text.

The label on the back of this device reads, "NON-COMMERCIAL PROTOTYPE". And a prototype it is indeed, as made obvious by the fact, for instance, that the holder for the backup battery remains unfinished, with no contacts found within. But it is a prototype that is functioning very well, and comes complete with box, adapter, cables, and a full manual set.

Revolutionary a device the Xpander may be, but is it a programmable calculator? That it is a calculator is not really in doubt, all you have to do is to look at its keyboard. As for programmability... well, sort of.

It is, of course, programmable in the sense as every Windows CE device is programmable if you can download programs to it. But those programs are developed using desktop computers and cross-platform development tools, so their existence doesn't make the device itself truly a self-contained programmable unit. But the Xpander also offers the ability to create user-defined functions that can later be invoked and executed. The Gamma function plot to the right was, in fact, produced by a user-defined function:

\begin{align}g(x):&=\ln\left[2.50662827563+\frac{225.525584619}{x}-\frac{268.295973841}{x+1}+\frac{80.9030806935}{x+2}-\frac{5.0075786397}{x+3}+\frac{0.0114684895435}{x+4}\right]\\

&{}+(x-0.5)\ln(x+4.65)-x-4.65.\end{align}

Whoa. That's a mouthful, isn't it. It's also an accurate method to compute the natural logarithm of the Gamma function to a precision of twelve digits for any positive x (with an error no greater than ±1 in the last digit, it appears.)

So why, then, am I reluctant to call the Xpander a true programmable device? The reason is simple: not unlike other educational calculators, the Xpander's formula programming provides no conditional or loop constructs. In other words, straightforward calculations are okay, but anything that resembles an algorithm is, sadly, out.

What I find the most impressive in this device is the built-in geometry application. Having just managed to construct a regular pentagon after a few minutes of experimentation, I have to say that it's a real pleasure to play with. The interface is fairly intuitive, and as a test of sorts, the pentagon did turn out as expected, with the last segment having the exact same length as the first.

Another impressive feature (the more I study this machine, the more surprises I discover!) is something new for a graphing calculator. Graphing a function given its equation is one thing, but how about a calculator that lets you sketch the graph, and then finds a matching curve?

For a prototype, the machine is also fairly stable. Not just the operating system (you would expect Windows CE to be stable, after all it's used in automotive applications and whatnot), but the main Math Xpander application as well. After hours of playing, I managed to crash the application only once, and as the Math Explorer includes some basic Windows CE tools such as the stock Task Manager, it was easy to kill and restart the frozen program.

In addition to the manuals, the Xpander also comes with a CD-ROM containing a Windows-based desktop application. Somewhat surprisingly, it is not Microsoft ActiveSync. The Connectivity Kit is simple, intuitive, and works very well; it lets you transfer files to and from the Xpander, and also capture screenshots like the one to the left here.

With all this in mind, it is difficult to comprehend why this project at HP "got the axe" at such a late stage during its development. From what I see, the Xpander stood a realistic chance at becoming a preferred device in many classrooms, helping HP regain much needed market share in the educational calculator market with a product that successfully demonstrates what that famed HP quality used to be all about.

Incidentally, the Xpander lives on. It is available free of charge for the Pocket PC, from Saltire Software.