χ² as a function of stellar population age for a comparison between STARBURTS99 SEDs and the integrated spectra of NGC2006 (blue) and SL 538 (red). Various lines types encode the SED metallicity with values for Z = 0.001, 0.008, 0.02, and 0.04 as explained in the top-left legend. The absolute minimum is located for both clusters at 14 Myr for a metallicity of Z = 0.008, however, from the shape of the χ² curve, the minimum is likely in the region between 14 and 21 Myr.