Spectra taken from a northern (M-SMA-12) and a southern (M-SMA-6) core to illustrate the shift in frequency due to the velocity component along the line of sight. The green, dashed vertical lines indicate the rest frequency of the J = 12−11, K = 0 transition. The core M-SMA-12 exhibits a blue-shifted velocity along the line of sight of 50 km s⁻¹, while core M-SMA-6 has a red-shifted velocity of 67 km s⁻¹. The systemic velocity of Sgr B2(M) is about 64 km s⁻¹.