I would like to run FEA on a single part. The part contains a cavity within it. There is a force applied along the top of the part. I would simply like to see the Volume or Δvolume of the cavity within the resulting deformed part after the load is applied. Is this possible?

I know how to view various output variables in the Simulation such as stress or displacement but I don't know how to set a custom output variable (i.e. volume).

EDIT: Can this be done with a sensor? I've never used sensors.