Graphmatica allows you to adjust the start and end of the x- and y-ranges independently, so as to create a perfect fit for whatever function you are graphing. Or, you can constrain one or more of the coordinates to produce a graph with a square aspect ratio without actually figuring out all of the values by hand.
Choose the Grid Range item from the View menu to modify the grid. To create a "custom" grid, estimate the top-, bottom-, left- and rightmost extremities of the graph, and fill in these values in the appropriate edit fields. The new grid may be somewhat expanded or compressed depending on the aspect ratio, but it will show the part of the graph you're interested in the best possible detail.
To create a "square" grid where both x and y axis have the same scale, just leave any of the four coordinates blank and mark the "Autoscale fourth coordinate" checkbox, and the fourth coordinate will automatically be scaled properly to fit the other three. If you pick the least significant coordinate to AutoScale, you can match the other three exactly, framing your graph almost as well as a custom range, but with a more natural aspect ratio. If you want to show the same range both above and below the x axis, you can leave both top and bottom coordinates blank, and they will be generated to fit the current aspect ratio.
Select the Reset button to reset the range to the default grid saved in your graphmat.ini file (the preset default is (-8, auto) - (8, auto)).
You can also easily change the range using only the mouse; see Selecting a Range with the Mouse.