Digital refractometers are optical instruments that employ the measurement of refractive index to determine:

Salinity of seawater or brackish intermediates
Model: MA887
Range: 0 to 50 PSU, 0 to 150 ppt, 1.000 to 1.114 S.G., 0 to 80 deg C

It eliminates the uncertainty associated with mechanical refractometers.