In the methods of magnitude estimation and magnitude production, numerical estimations of sensation magnitude are obtained for a series of stimuli of varied intensity. The objective of the experiment is to establish precisely the functional relationship between stimulus intensity and sensation intensity. To accomplish this objective, valid measurements must be made of both stimulus and sensation intensity. It is important that the validity of both stimulus measurements and psychophysical judgments of sensation intensity be experimentally demonstrated. This has traditionally taken the form of demonstrations of additivity and transitivity of measurements.