Fechner's Law, is a formula that describes the proportional relationship between physical stimuli and perceived magnitude. In other words, how we perceive the magnitude of physical processes acting upon our sensory organs and nervous system. Weber's law extends this into relative terms, where it describes the minimal magnitude change for an external stimulus to be perceived as different from another (just noticeable difference, JND.) This can be how much brighter a light source, louder a sound, saltier a broth, longer a line, etc. has to be to notice a difference