Vertex and Axis of Symmetry
The sliders h and v move the curve either horizontally (left or right), or vertically (up or down). Note that the line of symmetry "follows" the curve when it is moved horizontally, but stays in place when it is moved vertically. The slider s traces a point on the axis of symmetry. Note that the horizontal distance from this point to the right side of the curve (with respect to the axis of symmetry) is always equal to the corresponding point on the left side of the curve.