Plane Poiseuille flow

Hello, I am currently trying to run pressure driven (-dPds) Poiseuille flows, in the installation, it says :

The following example simulates a pressure driven (-dPds) Poiseuille flow (-Uwall 0) at the Reynolds number 1000 using a 1st order forward-backward euler scheme as initial time stepping algorithm (-is).

simulateflow -R 1000 -Uwall 0 - dPds -0.002 -is SBDF1 newfield.nc

I am a bit confused of the `-dPds -0.002 as I would expect that by fixing the Reynolds the code would already know the required pressure drop. ```