Accurate data for the concentration of dissolved oxygen in groundwaters is essential for documenting changes in environmental water resources that result from natural phenomena and human activities. Using the Rugged Dissolved Oxygen (RDO) probe with automatic temperature compensation and a portable meter, reliable measurements can be made in the field. For samples with salinity of 1ppt or greater, the meter can make a salinity correction for oxygen. See Electrode Log 54 Correcting DO Measurement for Salinity for details.