Measures on 2 Scales: Aquariums refractometer features Specific Gravity (D 20/20) 1.000-1.070sg and parts per thousand 0-100PPT (1‰=1ppt=1000ppm) | Seawater refractometer measures saltwater or salinity of water, ideal for aquarium, marine monitoring, fish-keeping,salty pools&spas and etc. | ATC Function: salty water refractometer with automatic temperature compensation, allow you obtain accurate readings easier and faster | Salinity Refractometer is made of aluminum body and ABS rubber light and very sturdy, comes with a hard plastic case, a mini screwdriver, a dropper | Easy to Use: put 2-3 drops on the saltwater’s prism, towards light then to get the accurate readings through the optic eyepiece, ideal for replacement the poor quality and difficult to read hydrometer refractometer