"Dry Hands" design avoids contamination of aquarium or water sample Takes a more "true" water sample at a 6 inch depth avoiding inaccurate surface sampling. Accurate to ?0.001 specific gravity & salinity (PPT) measurements. Auto-temperature correcting design. Durable construction for extended life. Designed to give a temperature-corrected reading in warm water aquariums - 68?F to 85?F (20?C to 30?C).