Instant Ocean Hydrometers new improved design delivers precise full-range salinity and specific gravity readings - accurate to 0.001 - every time. Easy-fill convenience keeps hands dry when filling. It has a durable, permanent needle mount and easy-read 2-color scale with safe zone and an extra-wide stabilizer base. Ideal for use in water temperatures of 68 - 85 degrees F (20°C - 29°C