The Mandelbrot Set

Zoom: To magnify a rectangular region of the image, press the mouse button at the upper left corner of the region, drag the mouse (while the mouse button remains pressed) to the lower right corner and then release the mouse button.
Reset: To return to the initial image, press the key "R" on the applet.
Image building delays: Building each image is a computationally intensive and hence slow process. To keep things reasonably fast, avoid building images with large black regions -- they are especially time-consuming to build.
Browser response time: The image computation is done by a separate thread that always runs at the lowest thread priority. Still, you might experience a time lag in response from the browser while the image computation is in progress.