Examples of SSP templates. Left panel shows 9 representative models from the MILES SSP library. These are labelled 1–9, corresponding to the position on the age-metallicity plane as shown in the right panel. The colourbar shows the integrated flux of the full grid of all 636 SSP templates as a function of age and metallicity. Younger stars are hotter and therefore brighter, explaining why integrated flux is a strong function of SSP age. Integrated flux depends more weakly on metallicity. For fixed age, we see that SSPs with greater metallicity have stronger absorption features e.g. compare spectra 7, 8 and 9 in the left panel.