SINAD (Signal-to-Noise-and-Distortion Ratio), ENOB (Effective Number of Bits), and SNR (Signal-to-Noise Ratio) are key dynamic ADC specs. SINAD is the ratio of the RMS signal amplitude to the mean value of the RSS (root-sum-squares) values of all other spectral components, including harmonics, but excluding DC. If SINAD is substituted in the formula SNR = 6.02N + 1.76dB, and the equation solved for N, ENOB results, or the effective number of bits. SNR is the ratio of the RMS signal to the mean value of the RSS values of all other spectral components, excluding harmonics and DC. Usually, only the first 5 harmonics are significant. SINAD and ENOB include all error sources and are a good specifications when comparing various ADCs. SNR is also important in many applications. Some manufacturers don't differentiate clearly between SNR and SINAD.  SNR is generally greater than SINAD. Also, some manufacturers may use SNR when they really mean SINAD.