Anyone who sat through "Top Of The Pops" a couple of months back and saw Trio yodelling through 'Da Da Da' will have spotted the razorheaded vocalist waving a foot long piece of white plastic, nudging it occasionally with one finger.

That was the Casiotone VL1 — a keyboard/sequencer/calculator/drum machine brought to you by the miracle of miniaturisation.

Originally conceived as something of an executive musician's toy, the VL1 or VL tone as it's sometimes called, very quickly found itself on record. The plinking background to 'Da Da Da' was the VL1's own rhythm box and several of the synth lines were played from its micro sized keyboard.

The keys are small black and white buttons half the size of a postage stamp and double as the 0-9 selectors for the calculator as well as plus, minus and other arithmetic signs and rhythm selectors for the drum machine. While the VL1's in its music mode, each white note played is represented by a number in the LCD calculator window on the left hand side. Black notes get a number and a sharp sign.

The VL1 can also be set to record a tune in two processes: first you play the notes in the proper order, but without the worry of getting the timing or the speed right. Then you select a drum rhythm and play back your tune using two small blue buttons on the top right of the keyboard, this time injecting the proper timing and feel which is stored in the VL1's memory.

The readout will display the drum machine tempo, adjustable in 19 steps from very slow (-9) to absurdly fast (+9) and the VL1 even has a pre-recorded tune loaded in at the factory which won't win any airplays but demonstrates the available drum patterns and all the five preset sounds — piano, fantasy, violin, flute and guitar.

Bum notes in your programmed tune can be easily deleted and the Casio will either insert a new one of your choice or join up the two halves of the melody.

And still there's more. The VL1 has room for one sound that you can manufacture. Each sound can be represented by an eight digit number, and every one of those digits controls a particular parameter and sets the strength from 0 to 9.

An accompanying Casio leaflet tells you what the figures mean, for example the first in the row of eight selects the waveform — 0 for a piano, 3 for a flute, etc, the next determines the attack time — 0 is rapid, 9 is slow, and then decay time, sustain level, sustain time, release time, vibrato level and tremolo level.

This entire eight digit figure can be stored in the Casio's memories and will stay there, along with any sequence you've loaded, even when the power is turned off. Incidentally, the VL1 switches itself off seven minutes after you last touched it so the batteries won't run down by accident.

It will only remember one patch at a time under the ADSR heading and though they're simply variations on the basic pre-set sounds you can have a laugh dreaming up your own noises — in fact the best results come from feeding in eight numbers at random and seeing what comes out the other end.

The sounds the VL1 produces through its own tiny built-in speaker are understandably miniature. The drum machine is not unlike the pinks and ponks of TV football games and though the synth can be shifted up or down an octave it doesn't sound that interesting until fed through an external amp via the mini jack output at the side.

One of the uses for keyboard players could be as a cheap 100 step sequencer though it's a pity that Casio have limited the number of repeats to four.

Still, at least with the LCD readout for tempo, you can make sure the sequence is at the right speed before you start.

Four penlight batteries provide the power and there's a mains adaptor socket at the back. The white plastic case measures 12in long by 3in wide by 1in deep, it's ridiculously light and portable and absolutely irresistible to any musician who wanders in the room and finds it sitting on the shelf.

Since the VL1 was first released, Casio have come out with even smaller brothers — the chrome finished VL10 which is literally pocket sized and the VL5 that can play chords of up to four notes on its tiny keyboard.

My favourite will continue to be the VL1, even though I never will figure out what it's supposed to be — a synth, a drum machine, a calculator or a sequencer. Only a pity it doesn't tell the time.

£39.95