1. Key in the function you would like to visualize into the input box.[br]2. You can click and drag on the 3D curve to zoom in and out, or rotate the curve to see it from all sides.[br]3. Use the sliders to change the values of a (x-coordinate) and b (y-coordinate) to see point P move on the surface.[br]4. Move the point to change vector u.[br]5. Observe how the value of the directional derivative changes as u changes.[br]6. Refresh the page if anything goes wrong.[br][br]