Dashed black lines – plot of errors (stddev) of CCF positions versus signal-to-noise obtained in 10⁵ simulations of simple spectra consisting of 1, 4 and 16 absorption lines (ordering is top to bottom). Solid black lines – expected trends due to Eq. (A.1) which is larger by approximately 8%. Note that the errors halve for each increase in the number of lines by a factor of 4. Blue lines are the equivalent results for a template A-supergiant spectrum, with the dotted line illustrating the explicit errors obtained from the simulation of Gaussian noise. The dashed blue line has been shifted upwards by 0.02 units for clarity.