Timing residuals of the simulated data files as a function of the orbital phase. A fictional binary with orbital period P_b = 2.45 h is shown on the left and the Double Pulsar is shown on the right. For all cases the original time resolution of the generated data files is TZNSPAN=1 min. Results with the originally installed 1-min resolution ‘polyco’ predictor are in orange, while in blue colour the results with re-installed ‘polyco’ with TZNSPAN=1 h resolution are shown. The upper panel shows the residuals after folding the originally generated fits files and reducing the time resolution by a factor of 60 (so that the resultant time resolution of the files is 1 min). The bottom panel is the same, but the time-averaging factor is 120 (2 min). The spiky features at phase ~0.25 represent limitations of the ‘polyco’ predictor, and become more pronounced as the time resolution of the predictor deteriorates and the sub-integration time (‘tsub’) increases. The effect is amplified for more relativistic binaries.