# Graphs on a spree

The graphic calculator is now used more and more in the secondary classroom on GCSE courses as well as at A-level where they have been fashionable for some years with students.

With the announcement by Casio of the CFX-9800G, a graphic calculator capable of displaying graphs in three colours as well as black, those students have a new "aspirational purchase".

This is not to demean the concept in any way; the use of colour will make it much easier to distinguish which graphs go with which equations. For example, if you are calculating the paths of projectiles and varying the angle of projection, you can define one equation of the path and outline it in blue, then define another using a different angle, outline its equation in green and see the two graphs in those respective colours. When combining waves, it should be easier to see how the components fit together to produce the final result.

Colour can also be used to show the areas in an integration or those defined by inequalities, and other operations such as zooming and tracing graphs become much easier. All that Casio, and the other manufacturers, need to do now is to find a way of increasing the number of pixels used in the display so that the graphs lose their annoying "steps" and everyone would be happy.

At the same time as pushing back the technical frontiers, Casio has announced a low-cost graphic calculator, the FX 7300G. This is basically a cut-down version of the larger 7000 series machines which I reviewed last year. It shares the same easy-to-use icon menu: you are presented with a screen of icons corresponding to the different modes and use the cursor keys to select the one you want. There is also a row of keys just under the display which gives direct access to functions such as range, zoom, plot, and clear screen.

The display is 80 by 48 dots which, while not exceptional, is more than adequate. The most-used graphic functions, such as rectangular co-ordinates, inequality graphs and statistical graphs are provided, but polar co-ordinates are not. Tracing along a curve, and drawing multiple graphs are easily managed, and the equation can be displayed on the same screen as its graph.

Programming the calculator is limited to 10 different programs, but this will be sufficient for most students up to A-level, and if Casio prices this machine sensibly, it will be a strong contender for secondary school and college use.

If you have one of the larger Casio graphic calculators (7700GB, 7700GE, 8700GB or 9700GE) it is now possible to share programs and data with a PC or Macintosh, using the FA-121 program link. The Mac needs to be running system 6.05 or higher and the PC at least Windows 3.1 or Dos 3.1. A cable is supplied to link the calculator to one of the serial ports on the computer, as well as the necessary software.

If you have seen packages such as Laplink, the transfer of files will seem familiar, being carried out via a split screen which displays the source and destination lists. You can transfer selected files or all of them, and a special fast process allows you to back-up the contents of the calculator onto the computer, although the files cannot then be edited.

A useful feature is the ability to capture a screen from the calculator, and to save it in one of the usual formats such as TIFF, bitmap or PCX. It can then of course be opened and edited in most standard drawing programs. Using this link is fairly straightforward and greatly adds to the versatility of a graphic calculator.

The final two calculators are improvements on existing models of scientific and fraction calculators. The AZ-45F is a simple four-function model with percentage, square root and memory keys and the ability to carry out operations with fractions. Four green buttons allow you to input simple fractions, the integer part of mixed numbers, to switch between decimal and fraction equivalents, and to switch between improper fractions and mixed numbers. The keys are large and positive in feel, and the display large and clear. This calculator will find a ready home in junior schools and the lower years of secondary .

The FX-115s is a fairly standard scientific model, with a 10+2 digit display. It can calculate in standard deviation, linear regression and complex modes as well as in different bases. The interesting feature is its ability (described by Casio as VPAM) to carry out calculations exactly as written; there is thus no need to decide which parts of an expression have the greatest priority, and calculations are greatly speeded up.

The calculator is, however, let down by the keys, which have a very loose and uncertain feel. It is easy to make errors while entering data. If Casio can correct this annoying fault, it will have produced a very desirable model.

Casio Electronics - stand 514

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