EVER TRIED adding up a slice of Bach? No, me neither, but apparently Musical Theory — chords, scales, progressions and stuff — is an elemental example of mathematics, pure and celibate. So, Musical Theory and The Calculator ought to make great lovers.

And so they do, coming together under the sheets of Korg's Chord Processors which use calculator technology to display hundreds of keyboard, guitar and score chord shapes. How they do this? On LCD screens which carry graphic representations of a keyboard/guitar/score and overlay small, black markers to show you where to put your fingers or write the dots.

The CPK-01 keyboard processor is the best example. Within the LCD window which takes up a third of the compact package are drawn three octaves of keys — F to E. At the top of the window is a horizontal list of all the root notes — C, Csharp/Dflat, D etc, up to B. You choose this root note by pressing one of two, small, left/right rubber buttons to the east of the window so moving an indicator arrow along the line.

At the bottom of the window are the possible chords split into four sections. These are (a) simple triads — major, minor, diminished, sus4 and augmented, (b) flattened fifths, (c) quads — sixth, seventh, maj 7, add9, those chords that require four notes to be fully rendered, and (d) tension chords.

The last, for those not so theory weary, are for adding 'abstract' notes to chords which, depending on your choice and interpretation, can sound anywhere from 'jazzy', through 'odd' to 'totally unusable'. Here we find the flattened ninths, ninths, sharpened ninths, flattened 11ths, sharpened 11ths, flattened 13ths and 13ths.

All these options are selected by further buttons (one each for 9ths, 11ths and 13ths) that will again step an indicator arrow through its paces along the base of the display.

Finally, the Korg will respond to two other tabs to give you four inversions for the simple triads and quads, and three for the complex tension chords. The accompanying Korg literature deserves a page in the Noddy book of poems at this point: "Chords which have tension notes are called tension chords." A miracle of explanation. Happily the unit itself is crystal clear in operation.

There are two failsafe's built into the CPK-01's logic. When, by dint of experimentation, you've requested a rare (weird) chord, an asterisk will appear in the top left hand corner of the display. This does not mean that the chord shown is unplayable, just that it's unusual. If you complicate it even further by adding a tension note, the display will start to flicker. But if you select a chord that's theoretically impossible — perhaps where the tension note you're requesting is already duplicated elsewhere — the display will go out and a small marker appears above the impossible bit of the instruction.

Korg give examples of maj7 (flattened fifth) and aug maj7 as rare chords, and diminished 6ths as impossible chords. I'll leave it up to your own ears to decide on the definition of rare.

A conclusion? Useful and, strangely enough, good fun. Often the reaction on seeing some of the more convoluted chords was "you have got to be kidding". But it prompted an effort and though, nine times out of ten, the reaction was "yeuch", the tenth was "hey, that's not bad". For such a device to answer all your simple questions and be creative into the bargain is quite a feat.

The primary disadvantage is that it obviously costs a lot more than a chord book. But it's smaller, neater, and easier to understand. You can at least see the shapes marching up the keys as various inversions are requested, and witness the tension chords being compiled.

With all this processing power at their command Korg could perhaps have given us a couple of bonuses — how about a display showing scales... major, minor, etc? All the info must be there. And it occasionally grows irritating if you find a desirable inversion and wonder what it would be like with, say, an 11th tucked on top. As soon as you press the button, the Korg leaps back to the first, common inversion and you have to step through the process again. Small detail, but there you are. Now how about the one with the hit single formulae?

KORG Chord processor: £33

CONTACT: Rose-Morris, (Contact Details)