The Weber-Fechner law (also known as Weber's law) quantifies "the perception of change within a given stimulus." This psychological law states the "change in a stimulus that will be just noticeable is a constant ratio of the original stimulus." It is a proposed mathematical correlation between the degree in which people feel the strength or intensity of a physical stimulus. Expressed as a logarithmic scale, it measures the difference between increases in magnitude as opposed to how those changes are perceived.
For instance, a person is exposed to heat and that heat is periodically increased. But as a person adjusts to the heat, he can feel the changes but generally perceive the changes as less than they actually are. Measuring the difference between the actual heat, and the subject's perception of that heat, can be quantified through the use of a mathematical formula.