## bel (B)

A unit of measure of ratios of power levels, *i.e.,* relative power levels. *Note 1:* The number of bels for a given ratio of power levels is calculated by taking the logarithm, to the base 10, of the ratio. Mathematically, the number of bels is calculated as B = log_{10}(*P*_{1}/*P*_{2}) where *P*_{1} and *P*_{2} are power levels. *Note 2*: The dB, equal to 0.1 B, is a more commonly used unit.