Weber’s law
a mathematical model of the difference threshold stating that the magnitude needed to detect physical change in a stimulus is proportional to the absolute magnitude of that stimulus. Thus, the more intense the stimulus, the greater the change that must be made in it to be noticed. This can be expressed as ΔI/I = k, where ΔI is the difference threshold, I is the original stimulus magnitude, and k is a constant called Weber’s fraction. See also Fechner’s law. [proposed in 1834 by Ernst Heinrich Weber]