Hagen Marina Minerva Digital Thermometer is an easy-to-read liquid crystal display (LCD) aquarium thermometer that is reliably accurate to plus-or-minus 1   F: no guessing, no color confusion. Mounts vertically & easily sticks to the outside surface of any aquarium.  Just place this removable thermometer in an easy to read position below waterline.   Approximately 3 4  inches  x  5   inches