Building tailored correlation templates. Top: reference synthetic PHOENIX spectrum (solid black line), with assumed limit on the continuum (solid red line). Line depth ranges corresponding to the weak, medium and deep templates are highlighted (in blue, green, and purple shades, respectively). Comparison with three observed Cepheid spectra, shifted in flux for clarity: δ Cep with HARPS-North (ϕ = 0.37, cyan line), β Dor with HARPS (ϕ = 0.33, yellow line), and ℓ Car with HARPS (ϕ = 0.38, orange line). We point out that these spectra have not been Doppler-shifted from the absolute velocities of the stars. Middle: corresponding weak, medium, and deep correlation templates (blue, green, and purple shades, respectively). Bottom: weighted ALL template (red shade). The default G2 template from the HARPS DRS (black shade) is added for comparison (see text).