A customary logarithmic measure most commonly used (in various ways) for measuring sound.Sound is measured on a logarithmic scale. Informally, if one sound is $1\,bel$ (10 decibels) "louder" than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibels corresponds to an increase of 10 x 10 or 100 times in intensity. The beginning of the scale, 0 decibels, can be set in different ways, depending on exactly the aspect of sound being measured. For sound intensity (the power of the sound waves per unit of area) $0\,decibel$ is equal to $1\,picoWatts\,per\,Metre\,Squared$. This corresponds approximately to the faintest sound that can be detected by a person who has good hearing. For sound pressure (the pressure exerted by the sound waves) 0 decibels equals $20\,micropascals\,RMS$, and for sound power $0\,decibels$ sometimes equals $1\,picoWatt$. In all cases, one decibel equals $\approx\,0.115129\,neper$.