Two spectra of CN-weak, CH-strong stars with different S/N ratio are shown as examples of our best and worst data: the upper spectrum in all panels has S/N ≃ 25 (on the S3839(CN) band) and belongs to NGC 1851; the lower spectrum has S/H ≃ 10 and belongs to NGC 6388. Both are shifted on an arbitrary flux scale for sake of clarity. The top panel illustrates the chosen windows used for the CN and CH indices (magenta hatched regions) along with their respective continuum windows (grey hatched regions); while the bottom panels show the windows adopted for the H and K Calcium index (bottom left) and the H_β index (bottom right).