AccuProbe ® Individually Calibrated Hydrometer A highly accurate, easy to use, wide range specific gravity meter for marine aquarium use. Designed to eliminate inaccuracy issues common with competitive quick-dip hydrometers while helping you take a water sample from a greater depth that is free of the negative impact of surface influences. Durable Construction For Extended Life "Dry Hands" design avoids contamination of aquarium or water Takes a more "true" water saple at a 6 inch depth, avoiding inaccurate surface sampling Accurate to ±0.001 specific gravity and salinity (PPT) measurements Auto temperature-correcting design to give a temperature-corrected reading in warm water aquariums - 68°F to 85°F (20°C to 30°C) Readings can be taken in or outside the aquarium Self-leveling, hanging device collects perfect samples Scientifically verified design offers the ultimate in accuracy