diff --git a/Examples/NSDebug.py b/Examples/NSDebug.py
index 7ed53df66a654d311b2095df9b57554018811039..2047a42e188c7a1439f407db7dcd809dcc86e8bf 100755
--- a/Examples/NSDebug.py
+++ b/Examples/NSDebug.py
@@ -152,7 +152,7 @@ for ope in distr.values():
     ope.discretize()
 
 # === Simulation setup ===
-simu = Simulation(tinit=0.0, tend=0.2, timeStep=0.005, iterMax=1000000)
+simu = Simulation(tinit=0.0, tend=1, nbIter=10, iterMax=1000000)
 
 ## === Monitoring operators ===
 monitors = {}
@@ -291,20 +291,20 @@ while not simu.isOver:
 ## print 'total time (rank):', MPI.Wtime() - time, '(', topo.rank, ')'
 
 
-print 'aaaa', velo.norm(topofft)
-op['correction'].apply(simu)
-print 'iiii', velo.norm(topofft)
+## print 'aaaa', velo.norm(topofft)
+## op['correction'].apply(simu)
+## print 'iiii', velo.norm(topofft)
 
-sref = op['correction'].discreteOperator.surfRef
+## sref = op['correction'].discreteOperator.surfRef
 
-flowrate = velo.integrateOnSurface(sref, topofft)
-print flowrate
-assert (flowrate - ref_rate) < 1e-10
+## flowrate = velo.integrateOnSurface(sref, topofft)
+## print flowrate
+## assert (flowrate - ref_rate) < 1e-10
 
-flowratey = velo.integrateOnSurface(sref, topofft, component=1)
-print flowratey
-flowratez = velo.integrateOnSurface(sref, topofft, component=2)
-print flowratez
+## flowratey = velo.integrateOnSurface(sref, topofft, component=1)
+## print flowratey
+## flowratez = velo.integrateOnSurface(sref, topofft, component=2)
+## print flowratez
 
 
 # === Finalize for all declared operators ===
diff --git a/Examples/postNSBluff.py b/Examples/postNSBluff.py
index 6a7280e57a8a210a635e3a0e376d83343a5af35a..1ca239dea031b916005a453605e7a609167a862c 100644
--- a/Examples/postNSBluff.py
+++ b/Examples/postNSBluff.py
@@ -60,7 +60,7 @@ def plotReprojection(filename):
 
 plt.ioff()
 direc = 'NSDebug'
-nprocs = 1
+nprocs = 8
 fileroot = direc + '/p' + str(nprocs) + '/'
 plotEnergyEnstrophy(fileroot + 'energy_enstrophy')
 plotDragAndLift(fileroot + 'drag_and_lift')
diff --git a/HySoP/hysop/operator/monitors/compute_forces.py b/HySoP/hysop/operator/monitors/compute_forces.py
index 00b0c59f3a25d26b8d3d50c593c24c1fe7940cab..64e6db21e78d6ca6d3b9cc4e2519551fe7a6b28f 100644
--- a/HySoP/hysop/operator/monitors/compute_forces.py
+++ b/HySoP/hysop/operator/monitors/compute_forces.py
@@ -50,9 +50,6 @@ class DragAndLift(Monitoring):
         self._dim = self.domain.dimension
         msg = 'Force computation undefined for domain of dimension 1.'
         assert self._dim > 1, msg
-        self._step = np.asarray(self.topo.mesh.space_step)
-        self._dvol = np.prod(self._step)
-        self._work = npw.zeros(self.topo.mesh.resolution)
         if obstacles is None:
             obstacles = []
         ## A  list of obstacles (rigid bodies) in the control box
@@ -64,13 +61,6 @@ class DragAndLift(Monitoring):
         self.force = npw.zeros(self._dim)
         # Coef in the Noca formula
         self._coeff = 1. / (self._dim - 1)
-        # function to compute the laplacian of a
-        # scalar field. Default fd scheme. (See Laplacian)
-        self._laplacian = Laplacian(topo)
-        # function used to compute first derivative of
-        # a scalar field in a given direction.
-        # Default = FD_C_2. Todo : set this as an input method value.
-        self._fd_scheme = FD_C_2(topo.mesh.space_step)
         # Set how reduction will be performed
         # Default = reduction over all process.
         # \todo : add param to choose this option
@@ -106,6 +96,17 @@ class DragAndLift(Monitoring):
         """
         """
         if not self._isUpToDate:
+            self._step = np.asarray(self.topo.mesh.space_step)
+            self._dvol = np.prod(self._step)
+            self._work = npw.zeros(self.topo.mesh.resolution)
+            # function to compute the laplacian of a
+            # scalar field. Default fd scheme. (See Laplacian)
+            self._laplacian = Laplacian(self.topo)
+            # function used to compute first derivative of
+            # a scalar field in a given direction.
+            # Default = FD_C_2. Todo : set this as an input method value.
+            self._fd_scheme = FD_C_2(self.topo.mesh.space_step)
+
             for v in self.variables:
                 # the discrete fields
                 self.discreteFields[v] = v.discretize(self.topo)