This technique required that the patient keep their hands immersed in saline to serve as a reference. Prolonged monitoring became feasible in 1974 when Johnson and DeMeester developed a dependable external reference electrode.[1] Using this technique to monitor esophageal acid exposure patients for periods up to 24 hours, DeMeester and Johnson were able to identify the most important parameters of esophageal acid exposure, and they developed a composite pH score to quantify gastroesophageal reflux. The initial 24-hour pH studies required hospitalization until the introduction of microcircuits in the 1980s that allowed portable esophageal pH monitoring in an outpatient setting.