The graph in the Liquidity module shows incoming and outgoing payments and the liquidity itself throughout the project. You can switch between a cumulative and a monthly view.
What the graph shows
Incoming payments and outgoing payments as separate curves, plus liquidity.
If the cumulative incoming payments curve lies above the outgoing payments curve, you are liquid throughout the project.
Switch to the monthly view to see which individual months are negative or positive.
This is how the graph looks:
Hover over the graph to see incoming and outgoing payments and liquidity for a single month.

