crystal-zoo Fish Tank Seawater Dual Scale Refractometer Salinity Meter 0 to 100 ppt 1.000 to 1.070 Salinity Specific Gravity Size about: 7.87 * 1.58 * 1.58 inch Measuring range: salinity 0 to 100 ppt, 1.000 to 1.070 Salinity Specific Gravity Minimum scale: salinity 1 ppt, 0.001 Salinity Specific Gravity Easy to use by reading the instructions carefully