Hold the left mouse button down as you drag the Slider control (labelled "Set Fade Level") above the image (or click on the arrow buttons) to fade between the IR and visible GOES/MODIS comparisons (17:10 and 17:12 UTC) on 07 April 2006. To zoom, click on the "Zoom" button, and then click the "hand" cursor on the image where you want to center the zoom. To quickly toggle between the 2 images, click in the center of the Slider control area, beneath the word "Fade" in "Set Fade Level".