Time-lag spectra at ∼2.55 Hz QPO frequencies from two LAXPC units, where lag-spectra of second LAXPC unit (LAXPC20; black points) is computed by choosing the reference band from the first LAXPC unit (LAXPC10) and vice versa (red points). The similarity between these curves and for the combined data (top middle panel of Figure 9) shows that instrumental effects such as dead time are not affecting the results.