Since working in a window that can be resized means that not only the size but also the shape of the grid can change at any time, the coordinates of the grid must be managed dynamically to prevent unwanted effects on the aspect ratio (simply put, whether a square on the grid looks square or is actually "scrunched" one way or another into a rectangle). Graphmatica has a feature to handle this called AutoSquare.
Whenever you resize the window, turn the point tables or data plot editor on or off, or turn the graph labels on or off, the dimensions of the grid rectangle change. To keep the grid square when it matches the logical coordinates to the physical screen, Graphmatica keeps the logical width of the grid the same and figures out how much height must be added or subtracted to maintain good aspect ratio. It then divides this height difference by two and adjusts both the top and bottom of the grid by that much. (This way, whatever point on the grid was centered stays centered.)
The state of the AutoSquare option has several important side effects as well. When you save an equation list and include setup information, Graphmatica checks the AutoSquare option. If it is OFF, the dimensions of the grid will be recorded exactly. If it is ON, at least one coordinate will be recorded as "auto" so that no matter what shape the grid is when you load the file again, it will be squared correctly. (If the top and bottom coordinates are equal and opposite, they will both be saved as "auto" so they will be regenerated that way; if they are not, only the bottom coordinate will be saved as "auto". The x-coordinates are always saved exactly.)
When you select a new range using the mouse and one of the Zoom buttons, Graphmatica also refers to AutoSquare. If it is on, the height of your selection will be modified automatically as you draw it so that square aspect ratio is maintained. If AutoSquare is off, you're on your own.
AutoSquare is ON by default. You can turn it off by selecting it in the Options menu.
When you turn AutoSquare off, the coordinates of the grid will stay the same no matter what size it is. However, this does not prevent the need to recalculate graphs before displaying them again, since to conserve memory graphs are remembered as a list of physical points, not logical coordinates. Future versions of Graphmatica may support translation of coordinates between different physical grids, making faster redraw possible (at the expense of quality), but presently it does not.
The status of the AutoSquare option does not affect automatic coordinate calculation when loading an equation list that contains a [grid] section. If AutoSquare was on when the file was saved (or it specifies "auto" for either or both y-coordinates), the grid will be squared. Otherwise it will be drawn with the exact dimensions it had when saved, regardless of x/y ratio.