JW's® Fusion Standing Thermometer for Aquariums features a weighted base with unique anchoring fins that keeps the thermometer upright and secure in the gravel keeping it in place. To use, simply drop the thermometer into your aquarium and simply push down into the gravel for secure placement. Features a Green Zone that tells you at a glance the optimal temperature range with a High-End Accuracy- (+/-) 1.5 F. for healthy environment range.