Line regulation applies only to series voltage references and is the measure of the change in the reference voltage as a function of the input voltage. The importance significance of line regulation error depends on the tolerance of the input supply. In situations where the input voltage tolerance is within 10% or less, it may not significantly contribute to the total error. The extension of line regulation over frequency is the Power Supply Rejection Ratio (PSRR). PSRR is rarely specified, but typical curves are usually provided in the data sheet. As with line regulation, the importance significance of PSRR depends on specifics the characteristics of the input supply. If V_IN is noisy (generated with a switching regulator, sensitive to EMI, or subject to large load transients), PSRR may be critical.