Salinity may be determined using a hydrometer to measure the specific gravity of sea-water. Calibration charts are provided with the hydrometer to convert gravity to salinity. Accuracy of hydrometer is to 1ppt. The use of a gravity hydrometer for salinity measurements can sometimes cause problems especially if you do not have the conversion tables. Therefore for convenience and accuracy Dryden Aquaculture have developed a conventional hydrometer but with a scale in salinity from 20 to 45 ppt in 1 ppt units.
Temperature can affect the density of water and therefore the salinity readings.
Correction factors are therefore included on the reverse side of the scale of the hydrometer to compensate for temperature.