Weber's Law

Weber's Law is a foundational principle of psychophysics stating that the smallest detectable change in a stimulus — the just-noticeable difference — is a roughly constant fraction of the stimulus magnitude rather than a fixed absolute amount. For example, if a user can reliably tell that a 100 g weight is heavier than a 105 g weight (a 5% difference), then at a 1 kg baseline they will typically need around 50 g of difference to notice, not 5 g. This constant fraction is the Weber ratio, and it differs across sensory modalities and stimulus types. In accessibility and assistive-technology design — particularly for sonification, vibrotactile displays, and haptic magnitude encoding — Weber's Law sets a hard limit on how many distinct levels of a stimulus dimension a user can reliably discriminate, and therefore on how much information can be packed into that dimension.