What is Control?
Control meaning The process of establishing a relation between a variable and one or more related variables. Correlation is simple if there is only one independent variable; multiple, if there is more than one independent variable. For gaging station records, the usual variables are the short-term gaging-station record and one or more long-term gaging-station records. (Searcy, 1960.)
reference: USGS – Water Basics GlossaryWhat is