Distribution of the differences between two independent redshift measurements of the same object, obtained from a set of 1192 VIPERS galaxies with redshift flag ≥2. Top: distribution of the velocity differences Δv = cΔz/(1 + z). Catastrophic failures, defined as being discrepant by more than Δz = 6.6 × 10^-3(1 + z), have been excluded. The best-fitting Gaussian has a dispersion of σ₂ = 200 km s^-1, corresponding to a single-object rms error km s^-1. In terms of redshift, this translates into a standard deviation of σ_z = 0.00047(1 + z) for a single galaxy measurement. In the bottom panel, the darker dots correspond to highly reliable redshifts (i.e. flags 3 and 4), which show a dispersion substantially similar to the complete sample (see text).