I quickly ran a simulation to check and clarify this issue.
I see that generating a chart from 'Monitors' for a calculated value, plots 'Convergence' vs 'Iterations' but essentially the Y-axis plots the Calculated Value only.
Below is an example to verify the same.
I gave an inlet velocity of 5 m/s to the geometry shown in the figure.
But when I generated a Calculated Value chart from 'Monitors', you will notice that the Y-axis shows the velocity magnitude indeed but 'Convergence' is written across it.
So this seems like an issue with the naming of the Y-axis.
I do understand this can be rather confusing. I will verify this with my team and see what can be done to correct it.