Fitness distribution of the iron pseudo-continuum fit of R136a3. The best fitting temperature (47315 K) is indicated. A temperature of 50000 K results in about the same fitness. The fitness is comparable to the inverse of a χ² : it is the inverse of the sum of the square of the residuals. The residuals are the difference between the normalised observed flux F_i and model flux F_mod,i, for all flux points of the iron pseudo-continuum.