Euler's method lets us construct antiderivatives numerically.[br]At a series of points, (x,y), I find the value of the function, and multiply by the width, [math]\Delta x[/math], to get the change in height, [math]\Delta y[/math]. The next point is [math](x+\Delta x, y+\Delta y)[/math].[br]This is building an antiderivative using the left hand rule.[br][br]The initial point and the value of the change in x are both controlled by sliders.