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On the left is a Casio fx-992V (from 1990), and on the right a Casio fx-992VB (from a few years later). I've had my fx-992V for longer than I can remember -- it was my go-to calculator for exam use, since everything else I had was programmable. Well, 'my' is a half-truth: the one shown is a now cut-and-shut job, with electronic guts from a donor calculator in worse cosmetic condition.

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Figure 1. Casio fx-992V and fx-992VB

The fx-992VB is a more recent acquisition, and it appears to be a facelift of the fx-992V. The main differences are the change in colour palette, and the rounding of the keys and bottom corners; personally I prefer the styling of the fx-992V. Otherwise, the two appear to have the same functionality and performance. Both are dual solar/SR927 powered (a.k.a. the Casio 'C-power' system). Both have the thin, light 4-layer Casio fx construction of the early 1990s (and the worn graphite battery contact pad -- see my post on the Casio fx-115N); Figure 2 shows the fx-992VB taken apart.

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Figure 2. Casio fx-992VB taken apart. From left: front cover, keypad membrane, circuitry, back cover

The fx-992VB is stuck into its wallet case with a glue pad. The glue is some nasty, gummy stuff that's nigh-on impossible to remove. When reassembling this one I just stuck it back on. On the other hand, the clear retaining bands used with the fx-992V's case are terrible (at least in my experience) for tearing.

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Figure 3. How the Casio fx-992VB is held in its case

The keypress of both feels more-or-less the same as the other fxs with the single-piece membrane keypad -- sort of like a shallow remote control. It doesn't have the positive click of e.g. HP Pioneers, but it's reliable and there's enough tactile feedback to know that the key has been pressed. On the fx-992VB the base selections are labelled above the keys, leaving no room for the left-arrow labelling the inverse-ENG function (which there is on the fx-992V).

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Figure 4. Differences in the ENG button. The fx-992V is on top, with the left arrow above the key

With such trivial differences covered, I'll stick to the fx-992V. It's got a high-precision 12+2 digit display, with optional ' marks separating every power of 1000. Values may have a maximum magnitude of \((10^{12}-1)\times10^{88}\), and the smallest representable non-zero magnitude is \(10^{-99}\). The parameter stack for operator precedence/parentheses is 6 deep. Aside from the usual scientific calculator repertoire of powers/roots, polar/rectangular, (anti-)logs, trig (good to about \(1.57\times10^{10}\) radians) and hyperbolic functions, we also have fractions, 1- and 2-var statistics, and a base conversion/bitwise logic mode called 'BASE-N'.

This isn't the fastest calculator. There's a noticeable pause between keypress and result when using things like trig functions, compared to the imperceptible delay on e.g. the HP 32S. Maybe this is down to power supply: the Casio has a solar cell and a silver oxide cell that lasts for years; the HP packs three LR44s. It seems these fxs were built more for efficiency -- but who needs instantaneous trig anyway? Memory comes in the form of the usual 'M' register written and read by [Min] and [MR], respectively (with the [M+]/[M-] for increment/decrement). There are 6 additional 'K' memories, also seen on other contemporaneous fx models. The value of the X register is stored to a K-memory using [Kin] [1]-[6], and recalled using [Kout] [1]-[6].

BASE-N mode supports 32-bit signed (two's complement) integers. Having a 12+2-digit display comes in very handy here. The current base (decimal, binary, Hexadecimal or octal) is shown in the exponent. For binary the value is shown in four blocks of 8 bits, with higher significance to the left. The block may be cycled through by pressing the [ . ] key, and the left four digits of the display indicates which is current (see Figure 5). Bitwise NOT, AND, OR, XOR and XNOR operators are provided. It's a shame there's no left-shift; the [\(x^y\)] key1 could've doubled for this. Of course, young me was plainly delighted at being able to use hex mode to write rude words on the calculator without having to turn it upside-down.

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Figure 5. BASE-N mode on the fx-992V, showing bits 17-24 of 1,234,567,89010

There are 128 physical constants built-in to the ROM. To use a constant, type its index number (from 1 to 128) and press the [CONST] key. From what I can find these calculators came with an index card for the constants to be tucked into in the case, but mine is long-gone. Frankly I've never been convinced of the practicality of this function and I don't recall using it 'in production'. If I have to find a constant in a table I might as well grab the nearest reference to hand and type it in, rather than hunt around for the calculator's manual or index card (assuming it's even one of the 128) just for the sake of a few keystrokes.

The instruction manual is adequate (and much like those of the other fx models). It covers all the functionality with simple, tight examples, but it is short and to the point -- of being terse. On the one hand the small size makes it convenient to slip into the case (just, it's almost too thick) but on the other makes it fiddly to leaf through, and bigger typography wouldn't go amiss. Languages are interleaved rather than sequential, which I find makes it tricky to search the manual without having to start at the table of contents.

Overall the fx-992V is a nice, no-nonsense professional's calculator. It's straightforward, precise and reliable, it ticks all the maths boxes, and packs them in a thin, light body. It certainly comes across as one the best non-programmable pre-algebraic logic infix models.

Footnotes
1 Yes, it does annoy me that this really should be \(y^x\).
The fx-992 models are interesting. They're basically the fx-991 of the corresponding series, but with 12-digit precision, 128 constants (a mix of scientific constants and conversion factors), and 32-bit binary support. I've got an fx-992S and the corresponding Radio Shack version - very nice non-programmable scientific calculators.
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