This nifty plotter won Kenn Garroch's approval

A plotter, like a robot, is one of those peripherals most computer users would like to have but feel they cannot justify the expense. The Parfitt plotter may be the answer as it is fairly cheap. Far from being just a flat bed plotter, it can be used for scanning pictures, milling shapes out of polystyrene, engraviong glass and, due to its flexible design, anything else you can think of.

The standard plotter comes with three pens, some paper, a manual and software on cassette. It measures about 58cm by 44cm and has a tasteful smoked plastic dust cover. The paper size is normally A4, though at a pinch it can be used with A3. However, not all the pens can then be used, due to their not accessing exactly the same area.

Each pen is slotted into a tube-like holder and lifted up and down by means of a solenoid. The pen holders are flexible enough to allow almost any type of pen, from the rather expensive fine-pointed plotter pens to low price Parker felt tip refills.

At the moment the plotter is available only for the RML Zs, the BBC B and (in future) for the Commodore 64. It is not hard to recognise that the system is aimed at the educational market.

The demonstration software came on disk and was fully menu-drive. Although these programs could have been better, they do their job well. Some of the demo options are: point to point plotting and pen selection, drawing of multiple polygons, an opto sensor scan routine, and some examples of what can be done with the opto system with a picture copied from a map of Britain and a gearbox cross-section.

Also supplied with the review model was Glassdem. This allows three dimensional wine, beer, or spirit glasses to be designed on the computer's display and plotted out onto paper.

The plotter was set up with a BBC B and connected via an interface to the user port. There is the option of using the BBC's own built-in power supply or, for those who happen to be running disk drives, there are two separate supplies available at an extra cost of £89.70 and £48.30. The more expensive version provides extra power for the milling attachment and has a rotary potentiometer for speed adjustment.

The most difficult part of setting the plotter up was adjusting the pen height. However, this is explained in great detail in the instructions.

Once the pens are in position, simply dropping them into their assigned tubes means the plotter is ready to start drawing. The Demo disk was autobotted and one of the options selected.

This is where the problems started. There was no precise explanation of where the origin was or how to get there. This meant that in some of the early drawings the carriage juddered against its stops and the software got lost, thinking that it has reached its desired position when it had jammed. The only solution seemed to be to press the BBC's escape key, thus rebooting the disk.

The review system seemed to get lost in other places as well. However, when I removed the Torch OS from the Sideways RAM and rebooted the whole system it worked more or less faultlessly.

After getting a little tired of the demo drawings, the next thing to do was to have a look at the direct control routines. These are all available to Basic via a set of CALLs:

Most of these commands are similar to those used in BBC Basic, so translating pictures drawn on the screen to the plotter is quite straightforward.

The major drawback with this plotter was its lack of speed, but adjustments were possible via the SPEED command. If the drawings were to be at all accurate, the best thing to use was the slowest possible speed which, for some drawings, meant leaving the system to get on with the job and coming back three to four hours later.

The opto sensor system is set up by replacing one of the pens with the sensor and using the supplied software. The computer then scans the picture line by line and transfers the monochrome result onto the screen. The best results were obtained with pictures that had a sharp black and white contrast although, with a little software aid, the results can be improved dramatically.

The milling attachment is meant to be used with polystyreene sheeets but produces pretty good results with baked clay. it has the advantage of being an educational tool as well as good fun. A full scale computerised milling machine can cost anything upwards of £10,000, but a simple plotter costs about £517.50 with a router attachment. The latter can therefore be used to demonstrate all the principles and their results at a 20th of the cost.

Another attachment is a scriber which can be used to engrave glass or scraper board. The best effects were obtained with mirror tiles. These were first coated with nail varnish and, after scribing, placed in etching fluid.

The best feature of this plotter is its versatility. It is possible to attach virtually anything to it that needs to be transported over a set X,Y area. At £310.50 for the basic model and £563.50 for the full kit including driller/router, opto sensor power supply and scriber, it is quite cheap compared with the competition. Though it could be more accurate, it is still more than adequate.