Comparison of the spectra for the HCN J = 2 → 1 (0,0,0) and (0, 1^1_c, 0) lines taken with the IRAM 30 m telescope in 1989 April by Lucas & Cernicharo (1989) (full line spectrum) and with the APEX 12 m telescope on 2015 May 28 (dotted magenta line spectrum). The bottom and top LSR velocity scales are appropriate for the (0,0,0) and the (0, 1 ^1_c, 0) lines, respectively. Both spectra have a velocity resolution of 0.26 km s⁻¹. The vertical bars give the relative intensities and velocities or the hfs components of the two lines. The intensity of the strongest component is normalized to T_MB = 10 K.