Preflare values of selected measures for 231 flares. Numbers in brackets indicate the ratio of confined to eruptive flares within the tested sample S​_M1+. (a) Unsigned helicity of the current-carrying field vs. unsigned total helicity. The dotted line marks the |H_J|/|H_V| = 0.25 level. (b) Unsigned volume-threading helicity vs. unsigned total helicity. The dotted line marks the |H_PJ|/|H_V| = 1.0 level. (c) GOES 1–8 Å peak flux (F_SXR) vs. free energy. The dotted line indicates the bolometric flare energy, using the relation log(E_bol) = 0.79 ± 0.1 log(F_SXR) + 34.5 ± 0.5 (Kretzschmar 2011). Blue and red color indicates confined and eruptive flare type, respectively. X-class and M-class flares are shown as stars and circles, respectively.