Absorption features comparison for H₁₀, H_η, H_ϵ, He I (4009.256Å), H_δ, and He I (4143.761Å). Each pair of spectra has been bootstrapped and radial-velocity corrected to be in the same rest-frame. The top panel of each figure shows the absorption feature spectrum portion for NGC 2006, while the lower panel shows the corresponding section for SL 538; the next panel below shows the normalized flux difference spectrum (NGC 2006–SL 538) and the bottom panel illustrates the flux ratio spectrum (NGC 2006/SL 538). The increasing noise seen on the right in some of the panels corresponds to the decreasing S/N of the spectra.