Average values of the four α-elements (Ca, Si, Ti, and Mg) in the bottom panel. Results of iron-peak elements (Ni, Cr) are shown in the upper panel. Clusters are ordered by [Fe/H]: NGC 4815 is the first cluster on the left, NGC 6705 in the middle, and Trumpler 20 on the right side. The errors are the standard deviation, σ, computed for member stars of each clusters. The colour and symbol codes are the following: green crosses for [Cr/Fe], blue stars for [Ni/Fe], red circles for [Si/Fe], purple filled triangles for [Ca/Fe], orange squares for [Mg/Fe], and empty salmon pink triangles for [Ti/Fe].