Gemologists use hand-held refractometers to identify gems. According to the International Gem Society, "a refractometer will also give you the birefringence and optic sign," further enabling accurate identification of the materials present in a gem sample. Quick field identification eliminates the need for transporting samples back to a laboratory for analysis.
Farmers and wine makers use hand-held refractometers to determine whether a crop of fruit is ripe, a critical step in deciding when to harvest. This precision is especially vital in the harvesting of grapes for use in wine production. According to Science Buddies, "[a] refractometer takes advantage of the fact that the higher the amount of sugar dissolved in the juice of a grape, the more the juice will cause a beam of light to bend, or refract." The measured amount of sugar detected is then checked against an established level to decide if the crop is ready to harvest.
For various reasons, but particularly for observation and conservation, scientists and conservationists measure the field interstitial salinity (FSI) of soil. This measurement is particularly crucial in the conservation of wetlands and marshlands, where too much salt in the water and soil can kill or drive away plants and animals. Obtaining periodic measurements of the soil to chart changes in salinity is essential to identifying threats to a marshland environment.