We define a true positive as a sensor response vector to an anomalous gas composition that is correctly labeled by the anomaly detector as anomalous. A false positive, or false alarm, is a normal sensor response vector that is incorrectly labeled by the anomaly detector as anomalous. Precision, which diminishes as the false alarms increase, is the fraction of sensor responses labeled as anomalous that are truly due to anomalous gas compositions: precision = true positives true positives + false positives .