the ratio of the just noticeable variation to the severity of a stimulant. Escalations in the severity of a stimulant which are just noticeably varied to the viewer are a constant fraction of the stimulant severity. The is computed by dividing the JND by the severity of the principle stimulant. The size of the weber fraction ranges as an operation of stimulant condition and sense modalities.

WEBER FRACTION: "The Weber fraction measures the intensity of stimuli. "