When you create a Global output, the Quantity will be automatically set to Solution Residuals.
Select which physics to assign the output to.
Set Type to Absolute or Relative (which is given by the current absolute value divided by the absolute value at the beginning of the simulation or time step).
Choose which residuals to display in the Outputs Summary after you run a simulation. The options will here will vary based on which physics you've assigned the output to.
For fluid physics, you can choose from Mass, X-Momentum, Y-Momentum, Z-Momentum, Turbulence, and Energy.
For heat transfer physics, Energy is the only option.
You can view the Outputs Summary by clicking on Outputs in the simulation control panel from within a simulation tab. You will see the summary in the properties pane below.