For the slope to be 1 on each step, we take a step in [math]xy[/math] of 0.25 units, and that should take us to the next contour line, as they are also spaced every 0.25 units. [br]The surface is defined by [br][math]z=\frac{\left(18y\right)}{\left(x^2+y^2+1\right)}[/math][br]If you orient into a top-down view, you will see the contours. Each equal-sized xy step will move up to the next contour.