  Large-scale bulk peculiar motions introduce a characteristic length scale,
inside which the local kinematics are dominated by peculiar-velocity
perturbations rather than by the background Hubble expansion. Regions smaller
than the aforementioned critical length, which typically varies between few
hundred and several hundred Mpc, can be heavily "contaminated" by the
observers' relative motion. For example, at the critical length -- hereafter
referred to as the "transition scale", the sign of the locally measured
deceleration parameter can change from positive to negative, while the
surrounding universe is still decelerating globally. Overall, distant observers
can assign very different values to their local deceleration parameters,
entirely because of their relative motion. In practice, this suggests that
information selected from regions inside and close to the transition scale hold
only locally and they should not be readily extrapolated to the global
universe. We show that this principle applies to essentially all Friedmann
backgrounds, irrespective of their equation of state and spatial curvature. Put
another way, the transition scale and the related effects are generic to linear
peculiar-velocity perturbations. This study generalises previous work applied,
primarily for reasons of mathematical simplicity, to a perturbed Einstein-de
Sitter universe.
