Free Scales
Free scales fill the available area using your maxima and minima. One unit on the x axis is very unlikely to be the same measurement as one unit on the y axis. For example, if we have a set of axes from -10 to 10 and draw them as free scales, the graph might look like this.
Equal Aspect
Equal aspect scales ensure that one unit on the x axis is the same measurement as one unit on the y axis. Using the same example, our graph might look like this.
Equal aspect scales are important for many graph types - especially polar. If you are not using equal aspect scales, many graphs just do not "look" right.
It is possible to get exact aspect scales to "fill the available rectangle". This is discussed in Tools / Preferences.
The equal aspect setting is ignored if your Cartesian function contains angle functions (eg sin, cos, tan) and you are not graphing in radians.
Fixed Scales
Fixed scales allow you to specify an exact number of millimetres per unit. This allows you to match existing graph paper for example.
Resizing
When you select Equal Aspect or Fixed Scales, FX Graph will produce a graph to your exact requirements. If you then place that graphic into another product (eg Word) and resize it, FX Graph has NO control over the output and your requirements will NO LONGER be met. It is much better to generate the exact graph you require inside FX Graph.