Comparison of the measured value for (top), resp. (bottom) to the one converted from the excess flux in the Ca ii IRT lines, using Eqs. (10)and (11). These plots include data from 2076 observations of 76 stars. The dashed line corresponds to the identity relation (top), or the zero-level (bottom). The Pearson correlation coefficient of converted to observed values is 0.97 in both cases, indicating a good conversion.