@Shakespeare The actual value of pressure doesn't affect other variable (thermodynamically) in incompressible case. What you care about is pressure difference, see Navier Stokes equation. Why not put a realistic value then? Apart from "why bother", if your pressure varies between 100000 and 100010, you are more prone to rounding errors than if you deal with pressure between 0 and 10. But whatever you reference pressure is, -163628, 0 or +19737, the results are the same