For both NGC 2264 (left) and DR21-W (right), lowest spectrum: absorption in the CH₃OH 2₀ → 3_-1-E line; other spectra: various maser transitions taken with differing velocity resolutions and a number of telescopes. Adopted from Menten (1991a). All spectra where taken between 1988 and 1990. The spectra of the 4_-1 → 3₀-E and 7₀ → ₁-A⁺ lines are from Haschick et al. (1990) and those of the 2₀ → 3_-1-E lines were taken with the Green Bank 140-foot telescope. The remaining spectra were taken with the IRAM 30 m telescope.