Sample mean of the real and imaginary parts of the cross-periodogram (top left and right panels, respectively), the sample mean time-lag spectrum and the relative time-lag bias (bottom left and right panel, respectively) in experiment PLD2. The vertical black and red dashed lines indicate ν_Nyq/ 2 and ν_Nyq/ 5, respectively. Above these frequencies, the LS102.4 (black curve) and LS102.4-2 (red curve) relative time-lag bias begins to noticeably increase (see text for more details). The horizontal dotted line in the bottom right panel, and in all subsequent plots, indicates the 0.1 (i.e. 10%) relative time-lag bias.