In this way, several teams of volunteers can collect samples simultaneously. If it is important to test in the field, meters designed for field use can be obtained for around the same cost mentioned above. As water becomes saltier, its weight increases although its volume does not measurably rise. Since salt water is denser than fresh water, this change of weight results in a greater specific gravity. The volunteer can calculate salinity by measuring a water sample's specific gravity.
Hydrometers are a fairly simple and inexpensive means of obtaining salinity.
Their greatest asset, however, is the high level of consistency they offer over time. The more dissolved solids in water, the slower light travels through it. Refractometers measure the change in the direction of light as it passes from air into water. Salinity and temperature both affect the index. Refractometers use a scale to quantify the effect that dissolved solids in water have on light.