HR diagram for the sources of the five star-forming clouds analysed in POISSON (see legend). Superposed evolutionary tracks for labelled stellar masses in M_⊙ (grey lines), isochrones for labelled time in years (blue dashed lines), ZAMS (solid red line), and early main sequence (dashed red lines) are taken from the models of Siess et al. (2000). The point with error bars shows the mean uncertainty on the position of the single sources.