Center-to-limb variations of the Q/I, U/I, and V/I amplitudes in Sr I (left) and Fe I (right) shown as black solid lines. The limb position is indicated by the vertical dashed-orange line. The estimated noise level is shaded in red. The CLV of Q/I is fitted with the function presented in the text, shown as a black-dashed line (for U/I and V/I the black-dashed line is set to zero). At this scale, the estimated noise level band in Q/I of Sr I is very small. For V/I in Fe I we additionally plot with gray lines the red peak averaged over ∼2 min and 15 spectral pixels. See text for details on the parameters a and b for the function (black dotted line) fitted to the Q/I CLV.