Weber Fechner Law is

The magnitude of the sensation felt is propoional to the log of the intensity of the stimulus (Weber-Fechner law) . It now appears, however, that a power function more accurately describes this relation. In other words, R = KSA where R is the sensation felt, S is the intensity of the stimulus, and, for any specific sensory modality, K and A are constants. P = K lnS/S0 (REF: Ganong's review of medical physiology 23rd Edition page no.153)