A quantitative representation in resistance units of the spectral density of a noise-voltage generator, given by R_{n} = (W_{n})/(kT_{0}), where W_{n} is the spectral density, k is Boltzmann's constant, T_{0} is the standard noise temperature (290 K), and kT_{0} = 4.00 × 10^{-21} watt-seconds. Note: The equivalent noise resistance in terms of the mean-square noise-generator voltage, e^{2}, within a frequency increment, f, is given by R_{n} = e^{2}/(4kT_{0}f).