ABSTRACT
The original form of what is known commonly as Weber's law states that δS/S = k, where S is measured in stimulus (physical) units, and δS is an increment on S with a defined associated probability value, usually .5 by convention, of difference detection between S and S + δS. It is thus a venerable measure of response uncertainty as a function of stimulus intensity, and implies that the response uncertainty increases approximately linearly with the stimulus input, where that uncertainty is measured in stimulus units. It is not actually a psychophysical equation, as only physical measures appear in it, and both sides of the equation are dimensionless.
