Position-velocity diagram of NH₃(1, 1) along the direction of the velocity gradient (E → W). At each offset Δα, the measured centroid velocities (V_LSR) are averaged across the filament in the direction S → N. The error bars (the standard deviation of the mean) result from this averaging. The different positions were weighted inversely proportional to the variance. The linear regression for the total range is shown by red: V₀ = −4.199(1)−0.000303(3)Δα (km s^-1) (here Δα is in arcsec). For the αβ condensation (−480″ ≤ Δα ≤ 600″), the regression line is practically the same. For the γ condensation (−1640″ ≤ Δα ≤ −800″), it is shown by a blue line with V₀ = − 4.38(1) −0.00046(1)Δα (km s^-1). The number in parentheses is the one-sigma (1σ) uncertainty in the last digit of the given value. The (0, 0) map position is as in Fig. 1.