Example: To determine the indifference curve leading to the utility level S = 20, cut horizontally through the 3D utility function at altitude 20. Project the obtained altitude line onto the wage/employment surface. This projected line is an indifference curve. Figure 2 redraws this curve in a 2D diagram.

Repeating the same exercise at other altitudes renders other indifference curves. Those indifference curves situated further north-east represent higher altitudes (and, therefore, higher utility levels).