Comparison between a synthetic (lower panel) and an observed (upper panel) colour−magnitude diagram for the horizontal branch of NGC 6723. In the lower panel, red circles are FG (Y = 0.248) stars (mass range 0.61−0.71 M_⊙), while green squares and blue triangles are SG with different values of the He abundance: Y = 0.248 and Y = 0.30. The mass range for the SG stars is 0.55−0.61 M_⊙ in the first case and 0.56−0.60 M_⊙ in the second.