Cumulative shift of periastron time relative to the predictions of a constant orbit caused by the decay of the orbital period. In the upper panel, the black points are the measurements of the periastron time shift, and the red solid line is the GR prediction, which is the sum of the GW damping calculated from GR and the calculated contribution from the Galactic acceleration and the Shklovskii effect. We display the residual between the measurements and the GR prediction in the lower panel.