How are residual calculated in MFIX?

How are residuals calculated in MFIX?

I see this in the MFIX output:

Timestep walltime, PIC solver: 9.718 s
Time = 8.07704 Dt = 0.10000E-02
Nit P0 U0 V0 Max res
1 2.1E-07 2.2E-08 1.9E-04 V0
2 1.4E-07 1.6E-08 1.4E-04 V0
Timestep walltime, fluid solver: 3.025 s
PIC NITs: 55 Total PIP: 399497

What does P0, U0 and V0 mean here?

Is it the residual for pressure, energy, and momentum conservation?>

      - P0    Gas pressure
      - PM    Solids phase M pressure
      - R0    Gas density
      - RM    Solids phase M density
      - U0    Gas phase U-velocity
      - V0    Gas phase V-velocity
      - W0    Gas phase W-velocity
      - UM    Solids phase M U-velocity
      - VM    Solids phase M V-velocity
      - WM    Solids phase M W-velocity
      - T0    Gas temperature
      - TM    Solids phase M temperature
      - GM    Solids phase M granular temperature
      - X0NN  Gas phase species NN mass fraction
      - XMNN  Solids phase M species NN mass fraction
      - K0    K-Epsilon model residuals

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Hello @cgw
Fluid velocity residual reaches the value of 3e8 during simulation. is it normal?