Colour-magnitude diagrams of NGC 6304 over-plotted with Victoria isochrones and ZAHBs. Similar to Fig. 4, but for NGC 6304. Panel a: Observed HST CMD compared to a model matched as described in the text. Model composition and RGB mass are given in the legend. Additional parameters are given in the top left corner. The reddening vector is shown as a black dashed arrow. Zoom box corresponding to panel (b) is marked. Panel b: Zoom on the HB. HB stars are marked with grey points. A ZAHB is over-plotted in blue with parameters as given in the legend, and the same ZAHB shifted in colour is shown in grey. The lowest luminosity HB star is marked with a diamond and lines extending from it are used to estimate the HB mass. The sloped dashed line is along the reddening vector. Note that depending on whether one shifts horizontally or along the reddening line, different stars are in this case the least luminous one.