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 = log10 (P1/P2) where P1 and P2 are power levels. Note 2: The dB, equal to 0. 1 B, is a more commonly used unit.