In physics, one-tenth ( 1 / 10 ) of a bel (B). Bel is a measure of comparative power, or loudness, i.e., a unit of relative power ratio. The number of decibels is the decimal logarithm of the relative power ratio, which is expressed mathematically as follows: dB = 10 log 10 (P 1 /P 2 ) where dB = deciBel, P 1 is the power level to be measured, and P 2 is the reference power level. If the result of the calculation is positive (+), there is a gain in signal power. If the result of the calculation is negative (