3D Graphing Calculator

This plots a surface, z as a function of both x and y, rather than a curve in a plane. Enter the coefficients of a quadratic in x and y, or pick one of seven named surfaces such as a saddle, a cone or a bell, give the rectangle to draw it over, and it samples the function on a 25 by 25 grid and paints that grid as a shaded isometric surface. Alongside the picture it reports the highest and lowest samples and where they sit, the height range, and for a quadratic the exact critical point and whether it is a bowl, a dome or a saddle, worked from the coefficients rather than read off the grid. The camera is fixed, so the picture does not rotate; that is the trade for drawing it on the server instead of in your browser.