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An interactive three dimensional plot with a downward facing elliptic paraboloid shown in blue. A point on the side of the paraboloid is highlighted in black. A selection of buttons at the top of the figure gives the option to change how closely the plot is shown around the highlighted point. The zoom level options go from 0 to 7, where 7 shows the surface for a very small neighborhood around the highlighted point. A checkbox at the top of the figure allows a plane that is tangent to the blue surface at the highlighted point to be drawn in red. The difference between the tangent plane the blue surface gets smaller as a larger zoom level is selected.