Fig. 5

Scatter plots for: (a) the highest Spearman correlation for WO₃ between E–WO₃ and Var6 (temperature of the furnace when the sulfur zone heater was turned on), Spearman’s ρ = 0.576; (b) the highest Spearman correlation for sulfur between E–S and Var7 (pressure), Spearman’s ρ = − 0.756.