Evolution of the eccentricity for the 3-body PN integration model. Initial positions and velocities were chosen from the full scale N-body model with N = 540k first randomisation at three moments of time in the first ZLK oscillation period from top to bottom: when orbital eccentricity for the inner binary S1+S2 was 0.5, 0.7 and 0.9. We individually turned “on” the different combination of PN terms in our 3-body PN code: PN0 (“Newtonian”), PN0+PN1, PN0+PN1+PN2, only PN0+PN2.5 and PN-Full = PN0+PN1+PN2+PN2.5 (i.e. with “Full”).