Complex sentence: Electronic noise is often measured in uV/root Hz, a term that derives from the fact that doubling the bandwidth of the measurement doubles the power level measured, but voltage is proportional to the square root of power.
Split into simpler sentences: Electronic noise is often measured in uV/root Hz. This term is derived from the fact that doubling the bandwidth of the measurement doubles the power level measured, but voltage is proportional to the square root of power.