Okay, I had solved the earlier problem in a different way but coming back to expressions now, turns out cell registers don't work either. n'gradient_vof_refine' is a predefined cell register. I have also tried similarly with other cell registers I have defined.nnAverage(VelocityMagnitude,['gradient_vof_refine'],Weight = None) gives - nInvalid locations( gradient_vof_refine)nnAverage(VelocityMagnitude,[gradient_vof_refine],Weight = None) gives -nRuntimeError: Average: Argument 2 is invalidnnAverage(VelocityMagnitude,,Weight = None) gives -nSyntaxError: invalid syntaxnnI have tried other Weights as well. Shows similar errors.nIs there any other way to make this work?n