The Penman Plotter is different from any other plotter on the market. It is a self-propelled drawing device that has more in common with a turtle than the normal flat bed plotters available for home micros.

The Penman is more, however, than just a socially ambitious turtle. Granted that it wanders about a sheet of paper under computer command and it draws lines as it goes, but there the similarity ends. It is capable of very reasonable quality drawing/plotting which is the equal of any plotter in the under £500 range. It can print text of any size, down to lower case letters only 1mm high. It switches between any of three pens, be they different colours or different thicknesses. It can act as a mouse for input, albeit not up to AMX standard.

I am not completely certain that this machine can't talk! I swear that it chuckles and mutters to itself as it scuttles busily about the piece of paper it works on. It certainly has the ability to stop and unravel itself if it gets close to being caught up in its own lead.

The originality of the Penman shows itself as soon as the package is opened. One is confronted with instruction manual, leads and a long, cream coloured, rectangular box. It turns out that the turtle itself is a quarter of this box, the rest being the interface and control software. pulling them gently apart exposes the pen sockets on the front of the plotter and the wheels beneath. A flat ribbon cable about a metre long also unreels - this is the penman's umbilical cord. The package design is of the highest order.

Apart from the solenoid-actuated raise/lower arms for the pens, the Penman has only two moving parts - two tiny electric motors equipped with optical encoders to read the amount of movement. A small recessed, freely swivelling tailwheel completes the triangle to give stability. Beneath the body are two slits for the positional photosensors. These are parallel to the edye which carries the pens.

Setting it all wup is simplicity itself. A 25 way 'D' plug set into the side of the main case connects via a lead to the RS423 serial port at the back of the Beeb. A small transformer supplies the power. You have to make certain, if you are to get the highest quality output, that the drawing surface is completely flat and level. It must also be firm and black. This is so that, using white paper, the Penman can sense where the edges are - it bleats and whimpers when it feels lost.

When the power is switched on the Penman is ready. If the serial lead is not connected it undertakes a short self-test, writing its name and drawing a set of interlinked circles. It then waits for instructions. Just before startup in computer mode the Penman has to be placed in a 'home' position, about two inches in and up from the bottom left hand side of the paper, facing the left. On startup it turns and finds the X-axis, moving forwards until a photosensor 'sees' the edge of the paper. It then gradually wriggles itself until it is satisfied that it is aligned parallel to the edge. It then turns through ninety degrees and repeats the process to align itself in the Y-axis. Then it moves to the centre of the paper and starts drawing.

You only have to see Penman draw a couple of straight lines and a circle to realise that the firmware, based on an 8-bit microprocessor, is very clever indeed. It rarely draws a straight line 'a la turtle' - driving itself straight along the 1line, drawing as it goes (though it can). The three main drawing pens are off-centre and it actually seems to go through a three point turn manoeuvre in order to keep the current pen moving along a straight line. The drawing action has to be seen to be appreciated.

The car drawing accompanying this article was the result of a program called 'MICAD' which has routines sending output to either a Hewlett Packard plotter or Penman. It probably shows Penman at its worst - not, I hasten to add, that this is Penman's fault. The circle/ellipse drawing routines in this program use a polygon procedure. This results in a lot of short juddery stop-swivel-start movements which have an accumulative effect of sending Penman off course. If you look closely you can see one or two points where lines do not quite meet.

The manufacturers recommend that 'homing' checks be built into any drawing process at reasonable intervals, usually after 400mm of movement. This sends the plotter back to the corner where it goes through the alignment process described earlier. Then with its position firmly in mind it returns very accurately to the drawing and carries on. In fact the MICAD program has now been updated to incorporate automatic homing at frequent intervals. However, this procedure slows down the plotting considerably.

The Penman can also operate as a 'normal' turtle and take its commands from Acornsoft's Logo. It has a fourth pen socket at its centre for this purpose.

Plotter commands for the programmer to incorporate in software are very simple and are dealt with quite thoroughly in the manual. It is easy to control as a robot - the accompanying software has example programs which put the Penman into a number of trial situations. These allow a number of interesting demonstration shapes to be drawn, bar charts, an orthographic elevation of a house, two animals, some very impressive Gothic lettering (true!) and a demonstration Logo procedure.

This program also allows practice use as a turtle, robot and optical input device. In this latter mode the Penman runs back and forth across a diagram and puts the information picked up by the photosensors on to the screen - crudely, but good enough for a demonstration for schools. There are also 25 Basic routines for Penman already defined for the potential programmer to incorporate directly into a program as needed.

The makers of Penman do not claim that this is a high quality plotter, suitable for volume output and business use. They intend it to be a plotter available to the average micro enthusiast at a price that can be reasonably afforded and they complement the plotting action with several other uses. The makers have, in my opinion, succeeded admirably in their aims. The quality of manufacture, the varied functions and the highly original design approach make it a very useful device indeed.