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The blue grid doesn't show up when printed or on overhead projection.
You can make the grid darker by graphing sin ax * sin ay = 0. Set a so that the solutions are the grid lines. In the default zoom, use a=2π. Darker2DGridLines.gcf demonstrates.
How can I label the x-axis in units of π?
You can label the x-axis by pasting pictures next to it. AxisInUnitsOfPi.gcf uses this feature to add labels at units of π.