Line-of-sight velocities (V_LSR) of the NH₃(1, 1) transition (dots with 1σ error bars) towards the ammonia peaks in the molecular cores L1512 and L1498 measured continuously in the PSW mode at the Effelsberg 100-m radio telescope in April, 2012. The exposure time at each point is 150 s. The position-switching offsets are shown in parentheses. The backend was an extended fast Fourier-transform spectrometer (XFFTS) with a channel separation Δ_ch = 0.039 km s^-1 (marked by vertical lines). Random shifts of the V_LSR values are revealed with an amplitude ≃ ±0.01 km s^-1 (i.e., ≃1/4th of the channel width).