Comparison of the velocity dispersion measured from the KCWI and SDSS spectra of the same galaxies, using the three “clean” stellar libraries. Note that SDSS and KCWI cover two different wavelength ranges (3600–5350 Å and 3600–4500 Å, respectively). The KCWI data have been convolved to match the SDSS seeing and integrated within the SDSS fiber for a fair comparison. Though the difference in the case of MILES is relatively large, we stress that SDSS data for these specific galaxies are not of sufficient quality to measure stellar velocity dispersions with precision and accuracy better than 5%.