The modification level of Al-Si alloys is generally evaluated by the depression of the (Al)-Si eutectic temperature which can be recorded by thermal analysis. However, this method requires a reference temperature which should be the eutectic temperature evaluated on the relevant phase diagram. Various methods proposed to account for the effect of low level alloying elements on this reference temperature are reviewed and emphasis is put on the so-called Mondolfo's equation which is updated. Predictions are compared to experimental information from literature.