A contour graph is a two-dimensional representation of a surface graph. This graph type is analogous to maps showing elevation. Just as you set the number of histogram bins, you can set the number of contour levels. This is done with the Z-Axis Options dialog box. Disable Auto Ticks and place the desired number of contour levels in the Major entry box.
You can also select the range over which the contours extend by first disabling Auto Scale and placing the desired range in the Min and Max entry box. You can also have logarithmically spaced contours by enabling Log Scale for the Z axis. Outward Ticks, Exploded Axis and Grid Lines options have no effect on a contour graph.