Cross-correlation in DIAdem: which channel is the reference and what does positive lag mean?

[55LVGA]

I have a question about how DIAdem defines the reference signal and lag direction in cross-correlation.
When I calculate the cross-correlation between two waveform channels (e.g., Channel 1 and Channel 2),

1. Which channel is treated as the reference signal at τ = 0?

2. When the result shows a positive lag (τ > 0), does this mean that Channel 2 is lagging behind Channel 1, or that Channel 1 is lagging behind Channel 2?

I would like to confirm this to interpret “leading/lagging” correctly in my analysis.