Weber Fechner Law is:

Magnitude of stimulus strength perceived is approximately propoionate to the log of the intensity of stimulus strength Weber - Fechner law It states that the magnitude of the sensation felt in propoionate to the log of intensity of the stimulus. Example - A person holding 30 grams weight in his hand can barely detect a I gm rise in weight (a rise than 1 gm would not be detectable). But when he holds 300 gm of weight. he can rarely detect a 10 gm increase in weight (a rise less than 10 gm would not be detectable to him. So a 300 gm wt. and (Say) 307 gm of weights would appear same to him.) This is expressed mathematically as Interpreted signal strength = Log x stimulus intensity + constant